My sister is homosexual and before that she was baptized but turned her back on God and now is "married" to another woman. Am I aloud to go visit with her like when she holds family dinners and things. Or where exactly do we draw the line. I have some family that says I'm wrong for not wanting to go to Thanksgiving because it's at her house this year and that family comes first.
My rule is to look at whether my presence would lead to a conclusion that I support sin. If I'm at a family gathering and a homosexual cousin shows up, that doesn't show my support for the cousin's sin. But in this case you are being invited to your sister's home. Going there would say that you find her situation to be normal and acceptable. The reason you are being pressured is because she wants you to admit she is right.
By the way, I would give the same answer for a sister living with a guy unmarried or a sister married to a man who has no right to a second marriage.
Personally, I would not go. Family does not come first. God alone is first. "Do not think that I came to bring peace on earth. I did not come to bring peace but a sword. For I have come to 'set a man against his father, a daughter against her mother, and a daughter-in-law against her mother-in-law'; and 'a man's enemies will be those of his own household.' He who loves father or mother more than Me is not worthy of Me. And he who loves son or daughter more than Me is not worthy of Me" (Matthew 10:34-37).
Fortunately the Christian is not limited to the family he was born into. "So Jesus answered and said, "Assuredly, I say to you, there is no one who has left house or brothers or sisters or father or mother or wife or children or lands, for My sake and the gospel's, who shall not receive a hundredfold now in this time -- houses and brothers and sisters and mothers and children and lands, with persecutions--and in the age to come, eternal life"" (Mark 10:29-30).
Thanks for the input. Do you have any other material on this? All help is very much appreciated. Also one argument brought to me is that they say that my sister knows they don't approve of them because they tell her they don't and that it don't matter what other people in the world think. But I think it does matter. Any Scripture related to that?
The problem is that your sister was a baptized believer. One can become unfaithful, but he is still a Christian. "Yet do not count him as an enemy, but admonish him as a brother" (II Thessalonians 3:15). Therefore, Paul's statement applies: "I wrote to you in my epistle not to keep company with sexually immoral people. Yet I certainly did not mean with the sexually immoral people of this world, or with the covetous, or extortioners, or idolaters, since then you would need to go out of the world. But now I have written to you not to keep company with anyone named a brother, who is sexually immoral, or covetous, or an idolater, or a reviler, or a drunkard, or an extortioner -- not even to eat with such a person" (I Corinthians 5:9-11). There is a reason why Paul said we have to sever social ties with a Christian who sins. Words are meaningless if a person's actions doesn't match his words (James 2:14-16).