I know, I could just say 'stop bitching, it's really unpleasant and it makes me not want to spend any time with you' but 2 things: I will probably just avoid saying it and it will just be put down to me being grump/bitchy to them/supercilious.
It is mainly MIL, although FIL and other family members join in. The bitching is fairly non-discriminatory in that everyone gets bitched about with one or two exceptions (even children!). It does have more serious consequences than simply bad-mouthing as far as I can see, or I would ignore.
I have told other family members that I will not go along with bitching about them, and whenever a conversation turns negative I tend to 'big up' the person in question or just flippantly say 'oh, I don't think that at all' and change the subject fast. This approach has simply meant that MIL only gets the 'bad stuff' about my DC (and myself!).
But the hint has not been taken...please help me! Can people change the habits of a lifetime?