I hope you reach out to good support groups, whether alanon, friends, family, anyone who might make your life easier while you have 4 at home and another on the way. Try not to stress yourself. You're taking care of 5!
Let the other one that needs on his own to take care of himself find his rock bottom. He's beyond your help. But the 5 of you aren't, so keep your priorities straight--you seem to be doing just that.
Congrats on another little one on the way. I only had one but wanted more. Maybe I can borrow a few of yours from time to time!