From this entire story, it appears your brother has some underlying anxiety and personality disorder issues that were undiagnosed, and expressed themselves under addiction psychosis. Cannabis psychosis is real, but the damage can heal over time (source)

As opposed to being ostracised and punished for his illness, your brother requires help - and judging from what's going on here, you might want to get yourself to some counselling to.

The point of what i'm saying - don't blame the cannabis. There's something a lot deeper happening here - most likely the stress being put on you and your family, other familial issues, and lastly don't discount genetics. Some of us - myself included - are sadly blessed with anxiety and personality disorders. I'm currently in Cognitive Behavioural Therapy, which has helped a lot. I also have a strong community.

CBD, on of the active components in cannabis is actually used to treat psychosis and anxiety in many parts of the world (well, most parts of America, anyway) SOURCE . It works.

I understand you're going through something difficult here, however, and won't turn this into bandstanding for cannabis advocacy. Seek better professional help.