Christine:
A tough and totally undesirable situation, to say the least. You seem strong, you have good instincts about how to handle this, about what is acceptable and what is not acceptable behaviour. With the right support, you can be armed to tackle these issues.
I think there are two main issues here, and you probably have already clarified these for yourself. But sometimes it helps to have others agree with you. It lends support of a kind, right?
1) your relationship with your husband
2) your husband's behaviour as a father.
His problems behaving as a father stem from his previous marriage and the divorce proceedings and fall out. It seems there were issues there that were never resolved. He has not set boundaries with either child. He has not taught them how to be responsible for themselves. At some time, he will have to be made to see that he needs to let his son take the rap. This may be the only way the son can finally learn that, as an adult in an economically prosperous country such as this, he is responsible for himself, but that he can expect support and encouragement from you both.
It seems that the best course would be counselling with a social worker for your husband so he can learn to set those boundaries. Primarily I think he should go to these sessions on his own, but that you should be invited to a couple of them so you can agree together on how to both be parents to these kids. He still has not really established himself as an authority figure in his children's lives, i.e. as a parent, not a peer. He cannot be their "friend" primarily, that has to come after being their parent. Otherwise, when will they learn to stand on their own two feet?
The son's drinking problem needs separate attention and yes, some rehabilitation/AAA program NOW, BEFORE IT PROGRESSES ANY FURTHER AND DOMINATES HIS ADULT LIFE, is required.
There seems to be another problem in that the kids are seen only as "his kids" and never as "our kids". The fact that the daughter always runs to daddy for back up and to get her own way is a clear sign that she is antagonistic towards you. She is doing these things to get at you, not just because she is an adolescent. Most adolescents still respect their parents at some level and this shows eventually. Your husband has not joined with you as a combined parental authority prescence. The girl does not see you as an authority figure at all. You currently have no "power" over her at all. She can see that, she has tested it and won. So, part of these issues is that your husband has allowed this second family unit to actually fracture into two in and of itself. There's you and your husband, and then there's your husband and "his" kids.
So, for the last issue, again some form of counselling will be required so that together you can sort out the balance of power, authority and equality in your marriage, as concerns your relationship with eachother and as parental figures for all three children.
There is too much going on here for you to possibly sort it all out on your own. You have already been established as a non-authority figure and as not on an equal footing with your husband anyway, so you need some counsellors to enter the scene as authority figures who back you up. Alternative balances of power need to be placed on the bargaining table.
No, don't worry, you didn't tell us more about your marriage than we wanted to know! Sometimes, our advice is just fishing in the dark if we don't know the full picture, or something close to it.
Good luck Christine and I hope all our support will enable you to re-negotiate your relationship with your husband.
Clare