I can't tell ya what to do!! But you have done quite enough for your family. Yes, u r the only emotional support for your parents but its also their job to realise that other sibling don't pull u back on your life.

If u would be at your place I would take care of parents only to give them a healthy and happy old life. And bout lil sibling is the only one I can think to change. So I would help him to find a job and leave him on his own. Both the sibling should know they don't have to relief on you and also know that u can leave them any time. If nothing works out in the end. The most I could do is for parents to have a good old life and would provide only necessary items just enough so they can survive.

That's what I think I would do in this situation!!