My sister-in-law and her live-in boyfriend have invited my family to their home for Christmas. My sister-in-law attends church most (although not all) Sundays and she sends her daughter to Catholic school, but she rejects many of the Church's moral teachings. She practices contraception and pre-marital sex, she finds same-sex "marriage" acceptable, and I believe she favors abortion rights. This is the second time she has moved in with a boyfriend since my wife and I have been married. She is still married to her estranged husband, and does not plan to finalize her divorce for another couple of years because she believes waiting will give her an advantage in the custody fight over their son.
My wife and I have a 4-year-old son, and we are trying to raise him as a devoted, faithful Catholic. We want to shield him from my sister-in-law's lifestyle as much as possible, because we do not want him to start to view such behavior as normal or as acceptable. We also feel like attending Christmas at their home would give the appearance that we find their living situation morally acceptable. It feels especially wrong specifically because it is Christmas. We are therefore considering declining their invitation. Do you think it would be uncharitable or unduly judgmental of us to do so?
Note: We initially invited them to our home for Christmas, but they insisted they wanted to have Christmas at their house instead and have already convinced a number of my in-laws to go to their house.