That's it really.
I think we need a network of mumsnet mums around the country, ready to mobilize quickly into small groups that can go out with video equipment and really get to the bottom of the AIBU classics.
Confront the errant MIL and read out all the "she's nuts" comments from the thread. Or pretend to be independent mediators and then agree with OP over MIL on every single issue to drive MIL even more crazy than she already is.
Weeks of fly on the wall to see if the recent vegan is a little more tediously vocal about her new vegan skincare lifestyle than she claims when pulling her husband up for his unacceptable rudeness. Or whether DH is the arsehole he appears, throwing a hissy fit because he's feeling insecure that his wife is happier and healthier and looks healthier.
They could even go into schools and hold teachers to account for failing to provide OPs super-intelligent DD with masters-level homework to challenge her amazing 9 year old brain.
AIBU is literal gold-dust and the only thing that could make it better would be being able to spend 4 hours a night on youtube assessing whether OPs in laws really are as insane as she says, or whether they're actually only a little on the odd side and it's OP who's batshit.
You are being unreasonable - people's lives would NOT be made massively better by AIBUs being followed up on youtube.
You are not being unreasonable - I'd save a fortune on streaming services if there was an AIBU youtube channel.