I have been in a similar situation with a friend. Can I ask, is it tobacco he’s smoking, or is he using marijauna? There may be some psychological damage from these unhealthy relationships, but in my experience, a drastic personality change is usually caused chemically (or by some unresolved childhood trauma resurfacing, but you haven’t mentioned anything like that)

As to your current situation, perhaps there’s a way you can bond with your brother without taking him too far out of his comfort zone? Are there TV programmes, films or sports that you could watch together with a bowl of popcorn or something? When initiating this, ask once, but when he declines (he probably will the first few times) don’t push the point – just say “Okay then” or similar and do the activity anyway. If he sees that the activity will continue whether he’s there or not, this takes the pressure off him and he’s more likely to engage.

Once you start being able to engage together, then positive energy will follow