How do I rid myself of this responsibility?

How to I rid myself of this responsibility?
I have been managing all of my brother-in-laws care and responsibility by myself going on five years after my sister passed.
I'm doing this alone without consistent help from any of his three ADULT children, or anyone else. There was ONLY one child that was consistent in visiting or CARING about him.
My sister asked me to take care of him. I made a promise to my sister on her death bed, a promise made under emotional pressures, not a life sentence.
I've honored my sister's request for FOUR YEARS (and counting)! I've done more than anyone could reasonably expect. And why does "he" expect me to continue doing all of this for him???
He lives in the same house as me, my adult brother and adult nephew. My sister and him moved in the house when she could no longer pay for her condo. This was more than' 10 years ago. I gave them the spacious area I used to live in because they were married and needed the space. I moved into one of the very small bedrooms in the house. When she died, he never said, 'here's your space back." He's still in there and only uses 1/4th of the space.

I cannot and should not destroy my own well-being to keep a promise that was NEVER MEANT to last forever. Because that's exactly what it is. Four years and counting of carrying someone else's responsibility, someone else's chaos, someone elses needs, on top of my own life. That's not a small thing. That's a MASSIVE emotional and huge burden.

Here's the part NONE OF YOU SEE: I DID NOT SIGN UP FOR THIS. I INHERITED IT. I WAS 'LEFT' WITH IT.

Four years and counting of doing everything for someone who isn't my partner, spouse, parent or child.
That's not caregiving in the usual sense. That's caretaking by default, because no one else stepped up.

He's had heart surgery and does not take care of himself as far as his diet, exercise or anything. He doesn't care.
I've been:
Managing his bills
Handling his checkbook
He is a Veteran, and I also keep a calendar and remind him of
medical appointments
I Fill his 'five' pill dispensers (I requested more medication from
the VA, because I did not want to fill the dispensers every week. He has 16 different medications he takes)
Fixing all the problems HE'S CAUSED
Carrying the emotional weight of my sister's last request
Absorbing the stress HIS OWN CHILDREN won't take on.
That's not helping. That running someone else's entire life.
It's no wonder I'm exhaused, angry and FEEL STUCK.

But honoring someone's memory doesn't mean sacrificing your entire life indefinitely!
I have to say:
This is too much
I can't keep doing this alone
Something has to change.

I've been doing this 'entirely alone; no one should be carrying this kind of responsibility without support.
When I say 'By Myself' it's not just a statement. It's a whole story in three words.

So, now one of his adult kids will have to take this over but they won't.
I suggested to one of his adult daughter's that he move in with her and she can start taking care of him.
She said, 'well there's really no room here in my house', but he can build a little house on our land! He cannot afford that!
His son lives in Virginia; his other daughter is useless (she lives in Wisconsin)
His brother and him discussed moving into an apartment together (he cannot afford that - he has too many financial responsiblities)
He cannot do anything on his own.
I'm 72 and he's 75.
I have no issues.
How to I rid myself of this responsibility?