WR it is very tough - but of course this terrible parenting example is a root cause of MLC. Doesn't mean everyone who was poorly parented has a MLC, as some people have the insight and courage to sort themselves out, but I never heard of a full blown MLCer that came from a functional family.
How are you going to handle the situation? Are you invited? If not then you have to be upfront with your kids about it and tell them to have a great time, but you are not invited.
To be fair to my MIL she was unwavering in her support of me (his father, who died before all of this was a piece of work, and until his death MIL (also now deceased) supported him, but when she was on her own she became a much nicer person. Sadly she and my xh remained unreconciled at her death, which is one reason why I believe his crisis is so prolonged
