Sorry to have read this but that doesn’t sound fair to me
Oof I feel for you! My mil and bil live in our house, she pays for both their expenses and his new car. He was tutoring his acupuncturist’s daughter in exchange for acupuncture up until recently (so no income), but now has a very part time admin job. He complains of having the care of his mom left to him, but both myself and husband work and have a son. Like duh, you can take that on! Sorry to take over your rant, you are not alone!!
Try and think of it this way the more your mum does for your brother now, the less you will have to do. You wouldn't want him to live with you if the worst should happen?
Its frustrating honestly. My mil babies her two daughters and is now stuck taking care of her grandbabies. And just now stopped paying for the oldest thats turning 27 in august. Its exhausting and frustrating if you need to vent more feel free to message me!!