I'm in a bit of a similar situation, and have to admit I feel a bit guilty about it. My grandmother, at the age of 90, is really getting old and feeble. We had to put her in the emergency room a week ago, because she was really out of it, and couldn't walk or even sit up. She's at a rehab place now, and slowly getting better.
My uncle lives with her, but he's not in the best health, himself. Goes to dialysis 3 times per week. He's 62, but not really a "healthy" 62. If I was to retire right now, I know I'd be on call almost 24/7, and it would make me miserable. I don't mind helping out with taking them to doctor's appointments and such, making sure Grandmom takes her pills at breakfast time on the days my uncle is at dialysis, and so on. But if I was on call all the time, I know I'd end up feeling trapped.
Also, I live right across the street from them, so I don't think I'd be able to retire on the downlow. Unless I made sure to leave the house all the time. Or at least, hide the car!
So, for the time being at least, I figure I might as well keep w*rking. it's an easy, low-stress job for the most part, close to home, and they're flexible with my hours. In fact, if Grandmom does come back home and needs more regular surveillance, I could get away with taking off on Tuesday and Thursday mornings to watch her while my uncle is in dialysis. But I just fear that once I do retire, then I'll start getting all the "Well you don't have anything to do, you can help out..." sort of requests almost non-stop.