Okay. I've read the majority of posts and it seems to me like you're desperately trying to force a relationship which is actually pretty toxic and fake.
You sound like, on one hand, you don't want to be involved (you talk of not liking the BIL) but then, on the other hand, you desperately do want to be included and are jealous when you're not.
Honestly, my suggestion would be focus on YOUR little family unit. Step away from social media, don't rise to the feelings of bitterness, jealousy etc as it'll just eat away at you.
You mentioned watching films in bed on xmas eve, but actually that in itself is PERFECT if you are content with that.
It sounds to me like you're unhappy deep down and almost trying to pin the blame on DH and his family issues and make them your own.
You're talking of gaslighting, but then you're actually adding fuel to the fire by getting worked up about this whole situation and probably causing DH to push them further away for an easy life.
I apologise if I sound harsh, I am not meaning to. I do totally get it, we had years and years of crap with my DH family..but you know what, a turning point was when I actually stopped caring. I stopped feeling angry and left out and jealous, I realised I didn't actually WANT to be around them..it was just FOMO....and I've totally made my peace with that.
This year, Covid regs make things tricky (or ideal, depending how you look at it) to keep your distance anyway.....and it sounds like the In laws are their childcare/support bubble? So they don't seem to be doing anything untoward.
Plus you mention your DH being outed for gross misconduct, so that is probably part of the reason too.
Make you peace with the situation, it will eat away at you.
Focus on the family the do matter, friends etc. It's never too late to build bridges, but I think expecting to be included in everything is unfair...people gather, people meet....the ISSUE these days is social media hilights everyones best bits and, if people are feeling down, seeing those posts can really feel like you're having your face rubbed in it.
Wouldn't it be nice if people could get together, have a lovely time, take photos for personal viewing and NOT declare it all to their facebook and insta followers..... [ grin]