living with cokehead schizo and I fear for my life

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Hey guys, I've tried to fix this problem myself but since that doesn't seem to be going anywhere I decided to come here. Though this problem started when I was twelve it has never been as bad as it is now. This person who I used to consider a brother on several occasions threatened to murder me, has pulled a knife on me, attacked my father, and most recently tried to murder my sister with a broken bottle. I really don't know what to do, I've tried talking to the police several times, I told them what he's done and that I don't feel safe but they've not been capable of resolving the issue. Every moment that I am in this house I feel on edge, it's gotten to the point where I can only get 2 to 4 hours of sleep a night and where I feel the need to carry a sharpened pencil just incase he attacks. I'm a high school senior who will be off to uni in a couple months, but I can not take this any longer, my parents also refuse to do fuck all about this. I didn't even feel this stressed when my brother hung himself. I tried to leave but I have no money and I also don't want to leave because I fear for the safety of my other siblings, what should I do?