Relocated to take care of 90 year old mother with degenerative kidney disease. Should I be paying rent to her + some of her expenses?

I, along with my three sublings have supported Mother financially for 50 years. She only has SS and prior to that had a very low paying job. My father died 52 years ago and she never remarried. We all helped her pay for her house, car, plus anything else she needed. Three years ago she became quite ill and siblings ask me to move in with her to help her stay in her home until the end. I was the only one, as they had families and lives. (guess I didn't)...I agreed after being 2000 miles away for 30 years. I always paid for 2 to 3 trips a year for Mom and siblings to visit me and made sure I was around for holidays etc. Continuing to send Mom money for her expenses. I am now the only care giver for a very critical, narcisstic, contolling, selfish mother (she was always this way). She demands rent from me and pouts when I can't pay for her food and perscriptions. She has demanded that I be given nothing upon her passing. This is fine with me, The price I have paid emotionally and physically the last 3 years will have to written up to another bad decision. Should I write up a personal care contract? She does not trust me, claims I do nothing for her, etc. She needs 24/7 care, I continue to put up with all the negativity....because my sisters and brother appear to give her money, appear in that my sister who has DPOA and total control of her finances pays for her "stuff" out of mother's money - not sure mom knows or understands what's going on. Brother in law let it out the other day during a "family" meeting. She has 20 to 30,000 along with a life insurance policy. As I was obviously at burn out stage - Mom does not want me to go outside, hates gardening, hates animals...would not let me drive her car (she no longer has a license) unless it was for her errands. Literally no life - she will not tolerate me even talking to people at the grocery store.....B's in law talked sister's into transferring the car ($5,000) over to me - they need me to stay sane so they can have a life....Mother calls them complaining if I'm gone for more than 1/2 hour, sleeping after 7 am. or staying up after 9 - they're tired of it - so they are trying to placate me with the car. They installed a life line - good thing...now they can go on to play golf at their homes in Florida. Mom has 6 to 10 months to live...and she would be tolerable if I gave her money (I don't have)....ok enough...what should I do? I have the option to pack up the "car" and leave - my other sister will take her in to her home..she has 4 very active sociable kids, 1 grand child, a very social life herself and a good husband - am afraid mom would attempt to destroy their lives too....any advice????