I would leave off the first sentence. Let that go unstated. I would say that my family has asked us to come for Christmas. I assume you and the kids would prefer to go to your sister's. How about I go to my parents' house and you go to your sister's? That way you are not condemning them for any past behavior. You are just saying what you would like to do. You could invite them all to go to your parents' house, eveb though we all know she won't go. Still, then you can say that they were invited. Otherwise she can say that you didn't invite her or the kids to your parents' house. And that's not the case, you were just jumping to the compromise without trying to pull everything in your direction.
