Not only is it reasonable not to want to be caught in the middle of your DIL and DD's disagreements, but you are entitled to ask them both to treat each other politely, if they meet in your house.
They are grown women who don't have to like each other or get on, but they do need to be polite to each other for the entire family's sake.
What does your son feel about these issues between his wife and sister? Surely, he could tell them both to behave!
If you bought a potato salad would you expect potato?


