<human>: My brother, Dave, is 32 and lives with my mom and step-dad. He recently moved back in prior to a move cross country at my mom's urging. He's been there for over a year and has no job or social life and barely talks to anyone, though he's always been a loner. He and I (29M) have never had a good relationship and he tormented me frequently growing up; he did plenty of things that I easily could have had him locked up for, including assault on me. Our family has always suffered from mental problems, mainly anxiety and depression, mixed with a healthy dose of substance abuse. Parents divorced in our early teens. 

Since moving out 10 years ago, I visit every couple months; having recently reached out to him (via phone, text and email) out of concern for his well being, he pretty much lashed out at me and accused me of conspiring with the family behind his back. At this point, I am pretty much at a loss as to how to handle the situation, due to his accusation and paranoia. I wrote him a long email explaining my motivation and logic with no reply. 

The problem is exacerbated by my mom, who had asked me to talk to him in her stead in the past. I refused and told her she needed to talk to him herself if she was concerned. From talking with my step-dad, it sounds like my mom is not handling the situation in a logical way; I am concerned about my brother and yet it seems she is pretty much enabling him. I'm not sure how we can get through to him at this point or where his mental health is headed (which seems like it's only getting worse.) 

Our dad is in the picture but has never had a healthy relationship with him - our relationship (my dad and I) is only now resembling anything I would call normal. He is concerned but was denounced in the same email from my brother where he questioned my motives and accused me of basically conspiring against him. 

Thanks if you've read this far, any advice would be appreciated.

Give me a shortened version of the text
<bot>: brother is withdrawn and living with parents who seem to be enabling him; he does not want help and mental health seems to be deteriorating.