Two examples of a young man's struggle with grief and the two ways it can go. The real brother, fallen into rage and cowardice, fully aware of the monster he's become; the rental brother, fighting hard against the dark for far too long and finally coming out the other side a proper man. Trying to help only ends up hurting everyone involved. Best thing to do is leave them the hell alone. Let them sort that shit out on their own.
Long story short: Get that kid outta there, and put that fool in a place where he can't harm others. You can call the police at this stage, but it's just gonna be suicide by cop. Something to think about...