Very sad that they think that having a relationship with their son requires "glossing over" anything. Parents can really not like something a child has done and still not reject that child. XH has pretty messed up parents. I hate to see your children having that example.
Regarding DS, is it really true you don't know? I'd guess XH brings GF and the kids because he views them as his family. He is unwilling to reject his family, nor, really, should anyone ask him to or expect him to at this point.
