My divorced parents are perfectly capable of it.

We didn't have regular "entire family" get togethers and holidays were separate, but they get along fine at things like graduations, my wedding, etc.
We don't do anything with bm. I doubt we ever will. She's sometimes capable of putting on the phony friendly face in front of the kids, but her family is not. at. all. They're very petty, self-righteous and generally hateful people. They all have control issues. They all are more interested in talking about people they hate than they are in talking about people they love. For as much as bm went for YEARS swearing to never be like her mother, that's exactly what she is. She parents differently and so I think she thinks that sets her apart, but it doesn't. They're just not nice people and they are not capable of taking the high road for anybody's sake.
Even if they were, though, it would just be very uncomfortable and I'm too much of an external feeler not to pick up on it and be affected by it. Dh has been assaulted by bm's mother in the past, which I think says plenty about how willing he would be to spend time with any of them. My il's have no interest in continuing a relationship with bm, but have never been impolite to her. Our side can only do so much, though.