An alcoholic's priorities are on his drinking, whether he's 'functioning' or not. The effect on children and family members can be profound, whether they live in the same house or not. I imagine his daughter has some pretty complicated feelings about her dad and has distanced herself.
My own husband was 'functioning' and did a decent job as dad to our kids (now teens) but in the wake of our separation I'm seeing a lot more clearly how damaging it was for them to have a dad who's an alcoholic.
Work on yourself and let the chips fall where they may. You have no control over your husband or his daughter. Have you checked out Al Anon? I found it really helpful. Also reading a lot about alcoholism. A great book is "Under the Influence" by Milam and also "Codependent No More" by Beattie. You may have a better understanding of your stepdaughter by learning about the family disease of alcoholism and how it affects everyone. It's like a play, with the alcoholic as the star and others in supporting roles, which all vary. Al Anon has some great free pamphlets that address this.