My brother is very mentally ill/sick/ parinoid. It’s getting to be very painful to watch/ overwhelming. How can I handle this?

My little brother who is 24 M has been sick for years.. suffering and depressed since he was about 15. Something shifted - he went from being a social, loving, goofy kid to a quiet, isolated, depressed + paranoia/ guy- I think for a number of things (smoking weed at young age/ adhd / etc) but it’s only gotten worse and I don’t know how to handle it anymore.. 

I am one of five and the second to last so come from a big family. I am not particularly close with my little brother anymore and he doesn’t live near me. He is currently visiting my parents and is worse then I’ve ever seen- it’s so painful to watch - I feel heartbroken about it and it’s killing my family. 

He shows no emotion, I haven’t seen him laugh/ cry in years. He’s parinoid, very depressed and struggling socially. No friends, no form of social life. He just got kicked out of nursing school for being creepy to a girl (I don’t think necessary his fault as he is socially very off) but who knows 

I feel for him in the way that this formed because of early on experiences. I want to help but my parents shut me out and get mad if I put in input- and I sometimes am honestly scared to be around him as he’s getting older and he comes off creepy. 

It’s hard to explain I almost feel like it could be early on schizophrenic- either way it’s horribly sad to watch. He’s been smoking a ton of weed, taking Xanax sleeping just in his room / binge eating. Has so much anger built up. Is difficult / monotone / creepy/ I don’t know what he is thinking half the time… 

I want to establish healthy boundaries (right now I am living with my parents because of a car accident I’m still recovering from) 

So I can’t runaway from it.. I hear everything about it. I’m a very empathetic person so it’s really hard for me sometimes to create a healthy boundary. 
There’s a lot of issues in my family and it brings me down immensely. I’m depressed about it - and so sad about my brothers situation.. 
I’m trying to work on myself and establish my own life but not sure how to break away from this SADNESS/ DARKNESS in my family. I love them and care for them but it’s getting crazy. 

Any advice or similar experiences would be appreciated thank you