How do I safely get out of this? I'm done with caregiving, but want to exit appropriately.

Sooner or later, I guess many of us hit the wall and have to admit, I'm in over my head and I want help or I want out. I've already tried the "want help" route for a long time, with no success -- for many years. I live with mom and up until recently, had shared POA. My sister managed to snatch POA under dubious circumstances and my other siblings are absolutely worthless and of no help and still expect me to spend all my time outside of work taking care of mom. Since sis took over, Mom isn't getting the medical care she needs, we are constantly battling to get mom to see her doctors and have access to things she needs, and the battle to remove sis as POA is beyond my reach. I have part-time help, but they do not work the hours I work, so mom gets left alone sometimes when I'm at work, and that means overnight, quite often. Oh, I have the luxury of caregivers here some hours when I am home; I know that makes some of you envious; but it's not when we need them here! Mom has already fallen several times. I happened to be home last night for her most recent fall, and that was my wake up call. What if I wasn't here? I can't get sis to add hours or change the caregivers schedule or to check on mom herself, even though she lives nearby. Any of those would be reasonable solutions, but they are not going to happen.
I need to "quit" my caregiving role -- my health is suffering in so many ways, and I have no life of own at all, get very little or no sleep, and I want to go back to just being mom's son again. How do I legally "wash my hands", and how do I cope with the reality that mom will likely suffer as a result of my actions? Is an email to sis and my siblings stating I'm done as of such date sufficient? Forget calling APS, mom's lawyer, talking about my own illness or expecting any reasonable response from sis with POA or my family. None of that will work. I'm the youngest and have routinely had to take on all the things no one wants to do. Sis won't even provide money for food for mom, and the only reason we got the caregivers part-time was because mom's neighbor threatened to call the police on sis to report medical neglect. If I thought I could go on and stay healthy, I would, but have come to the conclusion that it's just not possible. I can't leave my quit date open-ended, as family will just take advantage and stretch it out for as long as they can. But I don't want mom left unattended, either. The agency told me "behind my sister's back" they could have someone here starting tomorrow 24/7, so finding the help isn't a roadblock or reason to delay this past the weekend. Mom has the resources to pay, but sis controls the checkbook. It is going to have to be "forced", but I want to do this appropriately. I've thought about it for a long time and have already pursued and abandoned all other options I could think of, so I'm not going to change my mind.