paranoid schizophrenic?

I have a gut feeling that my brother might be developing or suffering from it. It's been going on for a while, we'd always chalk it up to angst or moodiness or he's a free spirit. But I dunno in the past year or so his behaviour seems to becoming progressively erratic and aggressive and he seems to be very delusional. At first he comes off as a stoner hippie so you think okay the nonesense he speaks is his hippie language, but then you really listen to what he's saying he sounds extremely paranoid, to the point he gets angry at has these panic aggressive tantrums about conspiracies, or people are reading his texts or stealing his ideas, that he's being oppressed and controlled. It sounds pretty nuts but I try to listen to his views. He's extremely withdrawn and extremely condescending like he knows the secrets of the universe so anything anyone says is wrong and he's right, and he will argue and manipulate you till you see it his way. Tonight he had a legit mental breakdown over a simple comment I made about him having lots of people in our house all the time (like allllllll the time :/) and he went nuts, screaming, throwing stuff around, crying, swearing, hitting things, shaking, pulling out his hair, rambling on about how he's trapped and no one gets him or cares about him. It was pretty scary. He's not one to break down that bad, he usually just slams the door to his room and play his rave music super loud when he's mad. But this was something else. I googled paranoid schizophrenia and majority of symptoms fit his behaviour. I'm not sure about the hallucinations (like voices talking) but I definitely think he's making up conversations like they are memories. He swears on his life I said something different which sparked the tantrum but my whole family was there and agreed that I never said what he thought I said. It's not the first time he's convinced himself of false memories. 

My question is, how would I know? Do you have any advice or stories to share? I'm not trying to bitch on here so no judgements or negativity, I'm genuinely concerned about his health.

Ps. He smokes more bongs a day than hours he sleeps. I know weed is connected to schizophrenia, my partners uncle is schizo because of it. I occasionally smoke it so I'm not ragging on it, just pointing it out.