How do I keep doing this every single day?

I moved in a year ago at their request. I have a 30 y.o. daughter who has special needs and I have recently been diagnosed with lupus as well as some other crap. I continued to work, a super stressful job managing a group home for folks like my daughter. I called home one day, there was a snow storm and I had to stay at the job. No staff could get in. My dad told me to put in my two week notice. After 20 years of doing that, I was pretty excited. I figured I'd get a nice part time job I didn't need to invest in so much (emotionally) But... That never worked out. First mom got too ill and her arthritis got too bad. I took over cooking, cleaning, laundry, med appointments etc...I was still ok because I could set them up with food I would fix in advance and go to Pennsylvania to visit my daughters and their children. Not long after one visit to PA my dad told me he misses me when I'm gone. ( Sounds nice, right?) The next time I go to PA, I start getting calls from neighbors that Dad is mowing and keeps falling down, they offer to help, but he keeps going. This is December 7, 2017. The first SNOWFALL of the year. Yup. Mowing in the snow. I rush home, he's broken his leg. I take him to the Ortho, he gets a cast...I go to Walmart with my son, he's walking around, no walker or anything! The foot is so swollen, I take him back to the orthopedic and they reset the leg. Several weeks later, I have the stupidity to go out with my son, first time in all those weeks, come back, his foot is HUGE. He's gone out in the yard in rubber gardening clogs! He rebroke the foot! Now he's got a huge disgusting fracture blister
(Google it, if you dare) and we're back at the Ortho again! I feel as they're manipulative and trying to keep me home.
Meanwhile, mom, whom I have never liked, for various reasons starting at the age of only a few months of age, sits in the corner in her mechanical and gives orders!
A week ago after him yelling at me like I never heard before, then claiming to not remember the next morning, I told him we were going to have to go to get some cognitive testing. He agreed. Until today. He's refusing to go.
I think I'm going to lose my sanity. I have two brothers who were smart enough to move across the country. So I'm pretty much on my own. My kids help as much as possible, but they have jobs and families of their own.
I can't leave. I can't just desert them. But holy cow! This is torture everyday from 7 am until 11 pm. I just can't seem to get it straight in my head that doing for good for others is a good thing. I know this. I've always tried to live this. But this situation is killing me and I feel like it had no end!