The way you left everything makes it sound like he's going to try and kill you in your sleep, try and really get your parents to understand that he really need more discipline and not try and stab people. I feel like your parents might be the best people to turn to, I feel like if you tried to talk to him it might just make him more agitated and then he really might not think twice about stabbing you, then again I don't really know your brother so I guess I really have no way of knowing how he'll react.
Leave him alone for a little bit though, don't be a dick and cancel his xbox just yet, even though he deserves it.