All you can reasonably do is help him get in touch with resources to help him recover.
And then, if he gets sober and starts to get his affairs in order, you can be supportive.
But his multiple severe challenges coupled with the fact that he has a family who could be supportive of him if he had been supportive of them lead me to warn you to limit your exposure here.
It's too much and you'll get overwhelmed, even if he's able to cope.
But being a supportive friend, knowing he has someone in his life who hasn't fully written him off can still be valuable.