Famzilla you might have seem me posting about my PILs, who seem very similar to your Mum.
One of my biggest regrets about the falling out with them was that I kept engaging with them and trying to justify myself. It does nothing but fuel the fire.
MIL behaves very much as your mother does, FIL seems to support and enable her in all of her worst behaviour.
DH's three siblings know what she can be like and two of the three have regular fallings out with her. The other says, as your brother has said, that we should all go along with her for a quiet life as she is too old to change. She's 61, she was only 48 when I met her and had been behaving in the same way as your mother since DH was a child. He's the youngest, SIL is six years older than him and says she remembers when her mother was different, but DH remembers nothing but this sort of control and manipulation.
It has poisoned PILs relationship with friends and relatives for years now. They seem to develop friendships that are instantly very intense and then fizzled out quickly, usually with PILs feeling bitter and complaining that everyone thinks they are better than them.
Since I stood up to PILs we have had the same accusation thrown at us time and again. You think you are better, you think you are too good for us, you are ungrateful, we have done this for you, you should do as we say, after all we've done for you, why do you hate us, what have we ever done wrong?
DH has spent so long listening to all this and being told that their mental health and emotional happiness are his responsibility and upsetting them will result in depression and a mental breakdown. He finds it hard to admit what they are like and I know even know he would rather do anything he could to 'make things right' than admit that they are the way they are.
I read the Susan Forward books, Toxic Parents and Toxic In-laws and she has some very good advice in them. I remember one story about a man who dared to go skiing with his girlfriend at Christmas rather than go back to his Mother's house for the holidays. He won the holiday in a competition I think, but instead of being pleased for him his mother spent days weeping and crying to his siblings, and to him on the phone. And the siblings spent their time fussing over her and ranting at him, telling him he had ruined Christmas for everybody and it could be their mother's last one and that he was selfish and cruel.
He was in bits by the end of it, and his girlfriend was ready to leave him because of the stress of it all. Their holiday was ruined but it wasn't just the holiday. When you have someone like his mother in your life, it's all the time. Constant pressure and stress if they feel like they are not getting their own way.
Susan Forward speaks about how this is common in families. It's easier for them to blame each other and make each other feel guilty than it is to admit your parents really are this bad and do something about it. Especially as nothing you do or say will change your parents behaviour, so all you can do is change how you respond to it. If someone stops 'playing the game' it means everyone else has to suffer and they would rather blame you than the person really causing all the upset.
She says everyone likes to think they had a good childhood, and admitting you grew up in a house with controlling, manipulative parents is hard. I'd really recommend reading her books because it makes a lot more sense when you read her own words. And she has a lot to say about guilt trips from parents who have "only ever loved you and done my best" that I think you should read.
And our situation is strange. FIL has admitted to SIL that he cannot cope with MIL's stubbornness or selfishness and the way she has to have her own way all the time.
I appreciate that he must be under pressure. But the way he has responded to it is wrong. He's let her put that same pressure on all four of their children from a very young age and hasn't stood up for them once.
I often wonder what life would be like now if FIL had ever said to MIL that she had to stop treating their now adult children the way she does back when they were small.
Instead he has chosen to try and make his own life easier by siding with her when she makes their lives harder.
As a result, their eldest is an alcoholic and drug user who has never had an ounce of confidence or self belief. The next is emotionally reserved workaholic who only relates to people he can get something from and who has emigrated and gone pretty much as far away as he can get. The third has never had a stable relationship, just a history of boyfriends who lie and cheat. And DH has always had self-esteem issues and low confidence.
The one thing I can suggest is sticking to your guns but without getting into long justifications of yourself, as they will only ever be twisted and used against you. You've done nothing wrong and the guilt trip is not your fault.