As someone with an older sibling who meets 4 of the 5 aforementioned criteria I can confirm that no it is not always that easy. Giving him a place on my floor wouldn't really do anything to improve his circumstances or outcome. What makes me the saddest is the realization that more than likely I will end up burying him in less than 5 to 10 years time. That sounds like a rather callous thing to say, but after watching my parents spend upwards of $100k on treatment program after treatment program it seems like there isn't any other choice but let him figure it out on his own. He's pissed away every opportunity he's had his entire life and it's time for him to take ownership of his own life. Not expect someone to always come running with an open checkbook.

I think that commenter meant that the family members with the home were the ones who had those problems (I've edited my comment to be clearer) -- but you raise a good point: sheltering a homeless family member with such problems wouldn't necessarily help them, and it may be significantly detrimental to your own situation.