My in laws are a lot like yours. If she was so loyal, y'all wouldn't be having that conversation about his daughter.
My in laws also loved to bring up my misdeeds constantly. I stopped going around them.
It's makes it very hard because I come from a broken home so we have spent every holiday and most Sundays eating with her family. They have become my family but I have got to accept the fact that they may no longer be my family. Been with them since my junior year in high school. They came to my basketball games and her dad has always been there for me. Such a shame but things change and life goes forward.
My wife really resents me due to thinking he has taken my side. I think one day she will respect that he is on the side of what is right. He has even told her that he would respect it if she would make a decision instead of continuing to be dishonest to me. He mentioned last night that this has been a strain on him and his wife. I will try to keep my distance as she needs their emotional support know matter what happens between us.