I think if you hadn’t made the “females” comment, you would have had a lot more sympathy op!
They do sound utterly dreadful, regardless of what gender they are. Yanbu.
After years of trying with some people in my dh’s family, (very long story), I recently had enough and have a “no big family events” policy, other than things I can’t avoid, like weddings, funerals, (god forbid, if we have any deaths) and christenings. Other than that, you’re right - nobody wants to be around gossipy, rude people who make them uncomfortable, even if they are related to their dp. Obviously they get special dispensation to a point, because they are related to your dp. But there does come a point when enough is enough.
For me, I now only see pils and not the rest, unless it’s totally unavoidable. Big birthday bashes? No thank you, I’m busy, but dh will be there to celebrate with you. Anniversaries? Ditto. I think they only invite me because they miss their scapegoat anyway, so no thanks!
Bit of a ramble there sorry, but yanbu, (except the “females” thing - one of my aforementioned ghastly in-laws is male and one of the bitchiest, most unkind people I think I’ve ever met).