I don't speak to any of "his" family because they are all feckin cheaters themselves and have always treated me and my (our) children like less than. So this is not something I will face in the future. I think you need to stay true to YOU. If this is not something you can handle right now, listen to your heart and decline. Choose you, Lord knows our WS and their APs sure do!!
I have thought about other events dealing with our children and I can only say that if he ever considers bringing his ugly skank to an event for one of our children he'd better bring back up.
My family is already bat shit crazy and doesn't need one more reason to confront him head on. He won't enjoy that confrontation, either.