What everybody else said and then some...
I know it's hard, but you're going to have to find a way to let it all go. You can't dictate morality or tell your siblings how to live their lives, and you wouldn't want them to do that to you, either. Your anger doesn't hurt them--but it will eat you alive.
I have one brother. My mother always thought he hung the moon. She hasn't seen him in months, and probably wouldn't even know him anymore. When he calls me now (rarely), it's usually for advice, and he doesn't even ask how Mom's doing.
Trying to force my brother to be the "devoted son" would be like trying to keep the sun from coming up in the morning. Can you say counterproductive? So we have an unspoken understanding--I call him when something major happens, and he defers to me on "mom matters." That way he can keep up the appearance of being involved, and I can do the DNR/Do Not Transport/POA dance without worrying about him challenging me. It's a win-win, and he's not down here every minute, slamming it on the table and telling me I'm doing it wrong.
My Mom was a royal piece of work long before the dementia, and always believed (still does) that I was put on this planet to comfort and take care of her
. And I guess in some ways I was.
At any rate, I made a promise to myself long ago that I would be there for her no matter what. I made my choice and I'm sticking to it.
I'm not going to tell you it gets easier as the disease progresses--it's still hard--but it's different
. You figure out ways to cope. Once I accepted that my "real mom" was gone, a lot of my resentments went with her. For us, it's too late for all that. I had to let it go. And I'm just too tired and too busy most days to worry about what my brother is or isn't doing. Sure, he can still **** me off like nobody else--that's my bro'! But I don't have the time to dwell on it
Hang in there, and don't worry--you'll find your own path, the one that works for you. And we'll be here cheering you on