Should I invite ex in laws?

This is one of the few times I would say that it's perfectly fine to be extreme. Usually I like to find a happy medium but in this case...just don't invite them. If she hasn't come to you to apologize why sacrifice every body's fun by throwing in these rude people who are just going to make EVERYONE uncomfortable? It's about your son. It's his day. Don't let this insensitive lady ruin it.