Can I get advice. Please. 😢

What do I do. It's a long story but here's a short version. My 82 year old grandma is stage 6 of 7 Alzheimers she doesn't know anyone. Can't talk, walk, feed herself (has a feeding tube) can't shower, go to the bathroom or nothing by herself. We have aids coming in and helping 12 hours out of 24 (the other 12 she's sleeping) anyways. My other grandma her daughter is about 64 and she moved in and left her house (her husband of 46 years lives in the house she moved out of) so she's here all the time, does running for my 85 and 82 year old grandparents (her parents) she dedicated her life for her mom. She has 2 other sisters and a brother. And her brother is here alot but don't help, 1 sister is all about herself and the other 1 is always going on vacation every other week so they don't come around.

Has anyone ever been in a similar situation. My grandma wants a few hours to herself but she won't let me do anything to help. Only when an aid don't show up that's when I can help that's it. And she looks after my 82 year old grandma, and a 5 month old. ( her great grand child it's my brothers baby) I feel sorry for her and don't know how much longer I can see her tare herself up and do this the rest of her life. 😢😢😢 ADVICE? ?? she has a big heart so she tells everyone yes.