Wow there are some delusional women on there, I can imagine my mil using somewhere like that to vent, dh has gone no contact with her and his awful sister for many good reasons but mil doesn’t see any of it, she is a functioning alcoholic usually but does have some bad episodes of black outs though I am convinced these black outs are very selective. 
Dh remembers mil and step dad coming back home once steaming drunk after they agreed he could have friends over while they were out. They both come back pissed as always, shouting and screaming and kicked dh head into a washing machine. Their version is this just didn’t happen at all (because 15 year old boys do make that up)
Both were very protective of his sister, she was not allowed boys round underage whilst they allowed him to have underage girls in his room and went out and bought them spirits to have (dh would of gone out and done it anyway so they were really being good parents apparently)
Multiple occasions mil getting drunk and chasing dh round the house verbally insulting him, scratching at his face etc. This didn’t happen of course.
Constant favouritism with his sister. Me and dh did not get engaged till two years into our relationship, mil reacted “why do you want to get married though?” We also didn’t get married till five years in. Dh sister meets a new man and is engaged within a few months and pregnant a the six month mark, que gushing about new grand child and how brilliant she is. I’ve never heard either of them say they are proud of my dh but sil is an angel the way they go on.
Because of all of this dh has always had a strained relationship with his sister which I can understand growing up seeing constant favourites played between you and your sibling. Again though they do not believe they played any part of this. Sil is very fake, feigned the whole aunty thing though it was more just to take pics of the kids and put them on fb. She and dh fell out and she dragged the kids into t, choosing to ignore them, my eldest is 8 and obviously noticed the missing messages and cards etc from this one aunty. Mil had excuses all lined up for her and honestly expected us to just forgive it 
We’ve gone nc with them all now and it’s the best thing we did, they are all toxic and enable each other’s mad behaviour, we are lucky we have my family. But yes gransnetdoesnt surprise me, I can imagine mil on there saying what an awful challenging child dh was and how mean I am. They are all mad as a box of frogs.