A tough spot for the cool uncle, but he still should figure out how to help Nana. It would be too sad to leave her suffering on her own. It's interesting the rotten old man did behave for a little while when he thought Song Hai was some triad gangster. So, I suppose if Song Shan subjected the old man to an old-fashioned beating, he might again behave. Typically an abusive parent experienced similar treatment in their own childhood, so violence doesn't solve anything, but since it worked once (or his imagined threat of it) in that particular man's case, there's no reason it wouldn't work again if it's not only left to his imagination.