My fathers family is like that, I have made the decision not to interact with them it's just not worth the Argo.
I think that families have their own dynamics. Some families are for each other through thick and thin, some get together when there is a threat to one of them, others enjoy the drama of conflict, others only want to be family through the good times.
I am not interested in going to family functions and pretend that all is wonderful. For me if the family is not prepared to dig together when things are tough then they aren't family, I just happen to be related to them.
Personally from what you have said I would not play their game and not go to the family function, it's not worth my peace of mind.