First, concerning our principles and practices. You do not seem to have a clear understanding of what our principles and practices are. It is overly simplistic to imply that we have a flat rule that there are no circumstances in which you can pray for, in the presence of, and, in some cases, with these people. This is explained in the book Church Fellowship: Working Together For the Truth and in numerous questions and answers in the archive section of this site. I will append some of this material below. You need to study this because you do not seem to have a clear understanding of our principles.

Secondly, you need to understand the teachings of their churches which are a threat to their faith. The main purpose of the principles of church fellowship is to warn them of these dangers. Simply to avoid praying with them, without them understanding why, will not help them. For example, the Catholic church teaches that we do not have forgiveness of sins through faith alone but by faith and works. This is a very dangerous error which threatens salvation. The Bible teaches we do not have to suffer in purgatory for our sins, the Catholic church teaches that we do. They teach we are helped by the merits of Mary and the saints and that we should pray to them. The ELCA believes that the Bible is full of errors. The LCMS has approved of ecumenical prayer services with non-Christians. You need to understand how these teachings are a danger to your loved ones' faith.

Third, you need to understand where your relatives stand in relation to these false teachers. Do your Catholic relatives pray to Mary? It should be obvious to you why you cannot join them in such prayers. Do they agree with the Catholic church's decrees which damn the Lutheran teaching of justification by faith alone? Do they agree with the pope's statement that the Lutheran church is not a real church but only a religious organization? If they do, isn't it clear that you are not agreed in religion?

Do your ELCA relatives believe that the Bible is full of errors? Do they support the ordination of women pastors contrary to Scripture? Which side are they one in the ELCA's battle over the ordination of homosexual pastors?

Does your father side with the more liberal party in the LCMS or with those who are opposing the deterioration? All of these questions have an effect on your private relations with them.

In short, you cannot help them until you have a solid grounding in how the principles of church fellowship are an expression of love that protects people from false teaching. The material below explains how you should approach them.

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A tract on prayer fellowship published by the WELS Conference of Presidents when our controversy with Missouri was reaching its height made these observations about the application of the principles of prayer fellowship in special circumstances with families.

Circumstances Vary, Principles Don’t

Those who advocate joint prayer between representatives of Lutheran synods that are not doctrinally one will not be able to obtain clear credentials for their practice. But does this rule out every joint prayer with members of a heterodox synod? Before answering that question, we must remind ourselves that on all occasions where Christians associate with one another, whether in public or in private, whether as synodical representatives or as individuals, the same scriptural principles apply.

What these principles are, this tract has set forth, namely, that it is always the will of God for his believers (a) to manifest in worship and in prayer the fellowship of faith that unites them (Ac 2:42; Eph 5:18 20) until and unless (b) confession of the truth and rejection of error require them to separate (2 Jn 10). These are not legalistic rules but evangelical principles. They are to be applied in the spirit of our Savior, who would not break a bruised reed nor quench a smoking flax. In both these principles, that of fellowship and that of separation, there is inherent the spirit of love and true concern for the spiritual welfare of others. In any given instance, we must do whatever the glory of our Savior and the true edification of the other person may require. This may direct us to join in prayer with others or to refuse to pray with them.

Now we know that there are devout children of God in all synods who unfortunately are not yet informed regarding the matters in controversy and are not aware of their involvement in error through membership in a heterodox synod. I may have an ALC grandmother who has always manifested a simple, childlike faith in her Lord and Savior but who nevertheless is unaware of the intersynodical differences and their implications. When I visit her in the privacy of her home, it might be a grave mistake were I to assert the principle of separation by refusing to pray with her under such circumstances.

What would the Lord have me do? Should I trouble her simple faith with these matters, which are apparently beyond her g.html? Or is it not my plain duty to support and build up her faith by praying with her or otherwise expressing my own faith?

If, however, my cousin is not only aware of the synodical differences but defends his church’s errors, I cannot pray with him—not even in the privacy of his home. In order to make clear to him that the error he defends destroys the unity of our faith, I must refuse to join with him in prayer. In cases of this kind, it matters not how close the other person may be to me as a relative or friend; here the word of Jesus applies: “He that loveth father or mother more than me is not worthy of me” (Mt 10:37).

There may be more occasions where prayer together with other Lutheran Christians or even with Christians of other denominations is indicated—in the hospital, for example, at the scene of an accident, or on the battlefield. When peril and imminent death reduce a Christian’s confession to no more than a .htmling, “Lord Jesus, help me,” we pray with that soul in his desperate need, even if he is not a member of our church body. When we stand in the presence of God, one in the awareness of our guilt and one in our complete trust in his saving love, we can unite in prayer as we could have united with the thief on the cross in his simple plea, “Lord, remember me.” Let us only be careful that we do not even then compromise the truth nor sanction error.

Finally, we dare not forget that there are those Christians who may be caught in an error, not willfully, but because their understanding of Scripture is insufficient. They are willing to bow to Scripture, but as yet, through human weakness, do not see clearly how the truth of Scripture necessarily rules out their error. What does God say to us concerning such weak Christians? He tells us, “Him that is weak in the faith receive ye, but not to doubtful disputations” (Ro 14:1). Receive, he says; receive such a weak brother and tenderly help him to overcome his weakness. “Receiving” such a weak Christian means that praying with him may well be in place and God-pleasing, and we trust that God will help him to grow in knowledge and strength. Certainly, this could not be done publicly without offense. And if such a person were to defend the error, even privately, then prayer with him would again be a denial of the Lord.

If we let these two principles guide us, that we manifest our Christian fellowship until confession of the truth and rejection of error require us to separate, then these concrete examples will not represent a policy of exceptions, but will constitute a truly biblical and evangelical practice.

We observe that even in the midst of the controversy with Missouri when there was valid reason for the fear that Missouri would try to justify lax practice as “exceptions to the rule,” our theological leaders clearly maintained the necessity of allowing for exceptional cases, which call for a departure from normal practice.

In a series of popular articles written for laypeople at the time when WELS broke fellowship with Missouri, Armin Schuetze warned against fellowship with members of a heterodox church:

Membership in a church body is an act of confession. Through his membership a person confesses himself to the teachings of that church. In joint expressions of faith that are public, such as, for example, public worship, prayer together in public, and going to the Lord’s Supper together, you would have to judge the other person on the basis of this confession of church membership, which is a public confession. To disregard this public confession would only create offense and confusion. Whoever is a member of a persistently erring church body needs to be avoided in all joint public expressions of faith.

In the next paragraph, however, he adds:

But now such a person from an erring church body is with you in your home, or you are in his home. From your private contact with him you know that he confesses trust in Christ as his Savior from sin, that he confesses himself to the Scriptures. It is apparent that his membership in the false church is the result of a still weak faith, which does not fully understand the seriousness of the errors, or it is clear that he actually does not share the errors at all. In this case you have more to go by than the confession of this church membership; there is also his own personal confession before you. And since now in your private personal relationship to him, public offense and confusion is not involved, you may well ask yourself, Is this person one of those of whom the Word of God tells you: “Him that is weak in the faith receive ye, but not to doubtful disputations” (Ro 14:1)? Is this a smoking flax that you are not to quench? Thus, in your private relations where public offense is not involved, you may on the basis of this man’s confession recognize him as a brother in Christ with whom you may also then join in prayer, and that includes table prayer.
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The following excerpt from the book Church Fellowship also deals with the issue.

Family and Friends

The principles which govern our practice of fellowship with individuals are no different from the principles which govern our public relationships with groups of Christians. We are to warn everyone who is holding false doctrine against that false doctrine. If they cling to that doctrine in spite of our admonition, we must not practice fellowship with them. It makes no difference if they are family or friends. We cannot place family ties and friendship ahead of our loyalty to God and his truth (Matthew 10:32-39; 12:46-49).

The one practical difference between the two situations, however, is that when religious fellowship with family or friends involves only private actions which will not give public offense, we may consider not only the public confession which they make through their church membership, but also their private, personal confession.

It is the public confession of their church which governs our public fellowship relationships with our family or friends. If they are members of a heterodox church, we must base our public relationship with them on the public confession and practice of their church. In other words, we should not participate in the services of that church with them, although there may be occasions when we attend services there as discussed above. As a testimony of love we must warn them against the false teachings of their church by refusing to participate in its worship.

In our private relationships with them, we may also consider their personal confession. For example, if they are dissenting members of a heterodox Lutheran church, who object to its false teaching and are fighting against it, we may recognize them as one in faith with us in our private relationships with them. We will encourage them to battle for the truth, but we will also warn them that they must leave that false church if their admonition is rejected. The private confession of faith which they make to us and the public confession which they are making by their church membership are in contradiction, and they must take steps to bring them into harmony.

If they are unaware of the unscriptural beliefs or practices of their church and, thus, are not knowingly adherents of false doctrine, we will urge them to become accurately informed about the teachings and activities of their church, which they are supporting by their offerings. Here too, they should take steps to remove the compromise from their confession.

If their private confession, however, reveals that they are aware of the false teaching of their church and defend it, we should not practice religious fellowship with them even in our private relationships. We must warn them strongly that their adherence to false doctrine is a barrier between us and them, and, more importantly, between them and God.

How should we put these principles into practice? First, let us consider our actions in our own home. There is no reason for a Christian family to abandon prayer and family devotions when others are present with them at the table. This is no different than having guests with us at church. The host may proceed with prayer or a devotion as normal. We have no more reluctance to have our prayers heard by others than Paul did on his voyage to Rome (Acts 27:35). Our prayer may be a good testimony and example to them. We may, however, feel that we should not force our guests to be a "captive audience" to prayers or devotions which they do not approve of, but this is a question of manners and tact, not an issue of fellowship. We must consider whether this is a good opportunity to expose them to the Word or whether imposing our worship on them without their consent will create resentment and a backlash against hearing the Word.

When we are guests at the table of a person who is not of our faith, and he speaks his prayer in our presence, we will permit him to do so without disturbing him, even if we cannot join him in his prayer.

We should not, however, join together in the prayers of adherents of false doctrine, either by asking them to lead our family in prayer or by joining together with their prayer.

The same principles would apply to a member of our church in a mixed marriage. If one spouse is a non-Christian, the Christian partner may pray for and in the presence of their non-Christian husband or wife. Obviously, they cannot pray together. If the other spouse is member of a heterodox church and ridicules or rejects the beliefs of our member, joint prayer is hardly possible. If the other spouse's membership in a heterodox church is seen as a matter of weakness in understanding, in the privacy of the home joint prayer may be possible. The Christian partner in a mixed marriage will try to win the other by a good example of piety and patience (1 Peter 3:1-7). Situations in mixed marriages may vary greatly, and the Christian spouse will be concerned not to do anything which is spiritually harmful to their partner. Much love, tact, and truthfulness is needed in such a situation.