What is the connection??
I'm not certain, but I have noticed a pattern over the years, with very needy and dependent alcoholic and addicted youngest siblings; and much more responsible, older siblings who take up the slack in serious ways. Someday perhaps I will do a survey. I think there is a way to take a poll on SR but not sure how that works.
Your brother sounds like me. I found out I was an alcoholic when I was about 29. The person who told me I had a problem was a person I trusted, whose judgment I respected, and who had five years in the Program. I argued with them at first, but it did not take long once I was presented with a few shreds of evidence, to admit that I had a problem. But, I am likely the exception to the rule. I just knew that if there was a remote possibility I was like my Dad (an obvious alcoholic), I wanted nothing to do with it.