Parenting the Parents

So it's been almost a year since mom died and things just keep going down hill here. I feel like I have become a parent to my own father. Maybe's he's just depressed, but since around December he has become impossible to live with. Refuses to talk, is grumpy, snappish, demanding, won't clean up or pick up after himself. I am beginning to feel like I live with a teenager. I am truly at my wits end here. Even thinking about leaving makes me feel guilty for leaving him alone, but am not sure I can do this much longer. My brother is even less of a help, every time I ask for advice, just mumbles "I don't know"