Oh gosh that is so hard for you especially with your DD moving away and being ill yourself.
I had the same thing with my parents for about 8 years. I had moved them to a warden controlled bungalow within walking distance of me as I am only child and previous to that they were a 2 hour drive away.
I was on call 24/7. I took my father to the hospital at 2 in the morning because his catheter had come out, I visited my mum every day for 6 weeks when she broke her hip, in fact visiting them both in two different hospitals in the same day.
I cancelled many holidays and weekends away at the last minute so it was a relief when they went into care.
My mother had severe dementia and didn't know me and my father was immobile but sharp as a button.
I found I had to limit my visits to three times a week as the strain was too much. My dad then died and I was diagnosed with breast cancer, fortunately my mother was totally unaware by this time to with Covid and treatment I only saw her about once a month. I was there for her 100th birthday there.
I feel your pain but as others have said - now your mother is in care limit your visits. It will help her to settle quicker and give relief to you. As your DH's brothers are coping with his parents I think you must distance yourselves for a while but also keeping in touch.
You cannot be all things to all men!!
Preston Davey, another baby P.

