Struggling with siblings in law

My husband and I raise our kids Jewish in the way we find most meaningful to us. We don’t keep shabbat but we do keep kosher at home, celebrate all holidays, and send them to a Jewish school.

My siblings in law both married non Jews. My BIL and his wife are raising their kids as Catholic. My SIL and her husband are exposing the kids to both religions equally.

Over time, this is starting to cause more conflict. They serve cheeseburgers at family gatherings. One year at Thanksgiving, the turkey turned out to be coated in butter.

Last year, we had a Hanukkah family get together and my niece said something to my daughter about Santa. My daughter replied that Santa isn’t real, just a man in a costume. Supposedly, my niece cried (I didnt see it but SIL claims she cried). My SIL confronted me about it. However, there is no way that I will be telling my kids that Santa is real to appease her. Honestly, the audacity is shocking to me.

I was wondering if others here had some insight on how to handle non Jewish relatives ​going forward. I purposely married someone Jewish because I didn’t want to deal with all of this interfaith stuff, but somehow I am stuck dealing with it anyways.