Tough love or tough it out?

My parents are in their late 70's. I moved back home a few years ago after losing my job, intending to stay only a short time until I got back on my feet. But when I got there, my parents' dysfunction took over my life (and became my dysfunction). There are too many deeply rooted psychological issues to go into here, but suffice it to say that I've been reliving all the toxic mental manipulation I endured as a child under their roof. What's worse, they've developed worsening physical problems that are preventing them from adequately caring for themselves and their home.

My father has a chronic autoimmune condition, has extremely poor balance and difficulty walking, falls asleep anywhere anytime (including driving) and takes countless medications. He shouldn't be driving at all, and recently I did limit him to short trips to and from the grocery, but my mother is "helpless" and has always relied on him to do everything for her. Everything that is except all the stuff I do - which includes all the yard work, heavy lifting, house repairs, shopping and preparation for my mother's book club, shopping and cooking for dinner parties for neighbors, driving on long trips, etc.

My mother likely has dementia or Alzheimer's that has recently become very noticeably worse. She has two siblings, a father and a grandfather with Alzheimer's. My mother refuses to be tested for dementia (despite acknowledging that she recognizes some decline in memory) and my father can't be bothered to have a conversation about anything, let alone anything of any significance. He's content to let my mother do or act whatever way she wants as long as his routine isn't interrupted.

I am at my wits end because they are the most stubborn, self-involved, heads-in-the-sand type of people you could imagine. They refuse to complete a will, despite my and my brother's incessant efforts to encourage and/or help them. They refuse to consider moving to a retirement community where they could be transferred to assisted living if need be. These character traits are longstanding, but time is short now. And it won't be long before something happens, or before my mother isn't able to make decisions for herself. My father has bouts of extreme confusion as well. Honestly I wouldn't know where to begin to take care of matters if/when that happens as I don't have the details about their finances.

I have been trying very hard to get them to make their own decisions both for their own sake and for the sake of their children, but they won't. If I push the issue, my father gets angry and threatens me and my mother throws tantrums and tells me to leave. But in the past whenever I have "left", she tantrums, stalks me via phone or email, calls my brother obsessively, etc.

So...in good conscience, I feel like it would be irresponsible of me to just leave, knowing that they can't take care of themselves; however, this is killing me. I am not in a financial position to "just leave" because all of my time is eaten up by these issues. My brother thinks I should take any job I can and just leave asap, and who cares if they don't finish the will. He thinks if I don't leave, they'll never admit they need help. I think they'll never admit it anyway, and if I do leave, I'll be stalked and harassed again, or they'll hurt themselves or someone else, and then I'll be the one who has to go back again and pick up the pieces. My brother has a family and lives many hours away and isn't in a position to take them in. I am single and so the burden falls to me. But I am near 40 and feel I've wasted most of my life dealing with their issues.

I don't know what to do. Any advice?