I don't think the things you are dealing with are trivial! I'm sure it is very hard to see your parents declining. Alzheimer's decline is very difficult for loved ones to watch. I'm sorry about your friend's mother, too. All of this, plus the job is a lot. Your son will do what he's going to do--whether or not you are there to watch him. It's great that he is doing well, working, and going to therapy!
Take time for yourself while you are with your parents--even just a shower or a walk around the block can help clear your head. A few months ago, I went away to take care of sick relatives. The physical and emotional stress is exhausting. I didn't have much time for myself, but even a small recharge helped.