It sounds to me like you have a three way marriage-you, your husband, and his ex wife. Your husband is afraid of his children not loving him, yet they only see him as a source of money at Christmas. According to psychologists, divorce is the second most traumatic thing a human being can go through, topped only by the death of a child. These children are caught in a terrible situation, between a mother who uses them to vent her rage, and a father who is not standing up for them. Everyone is so busy reacting that no one is thinking. As the "outsider" of the group, YOU are the one who is in a position to have a TREMENDOUS amount of influence over the situation, all you need to do is take a step back and think it through.
It's obvious you care a great deal for your husband and step daughter, or you wouldn't be asking for help. That makes you the strong one. Never underestimate the power you have because of your asking for help. You can be the rock in a world that's out of control, and you DO have the influence to turn this situation around and turn it into something wonderful, but first you have to realize that a lot of damage has been done and it's not going to get better overnight.
As a teenage mother myself at fifteen, I know how it feels to be pregnant at that age. I also know what it's like to grow up in a deeply traumatic household. My mom micromanaged everyone, especially me, and my dad tried to stand up for me, but always ended up going along with my mom because she would just wear him down. I ached for stability for most of my childhood. It was so frustrating, wishing so much that someone would see me as a person, not as something that needed to be "broken" and controlled. I was just an extension of my parents' illness. Occasionally through my childhood someone would pop out of the woodwork, sometimes a teacher, sometimes a friend, that somehow managed to see through the emotional mess that I had become and saw that I really was a decent person, and that I had value and ideas of my own that weren't so bad. I always remember those people as lifeboats, it meant so much to be seen as a person, not as a problem.
When kids, especially teenagers, act out, it's a cry for help. This poor girl is drowning in the battle between her parents. Has anyone sat her down and asked her how she thinks or how she feels? Sure, the first few times you ask her she's going to scream and yell and try to push your buttons. Children of divorced parents are deeply confused and traumatized. They see their parents fighting and can't decide if they think it's their fault that parents got divorced which makes them a bad person, or confused because suddenly they are supposed to choose one person over the other. They are caught in a storm where no one sees the damage that's being done.
As a mother, even a step mother, I'm sure it's difficult to resist trying to run a child's life. They might be 50 years old, but to a mother they are still a baby. That's why women make good mothers. Sometimes, though, it is important to remember that even though they are our children are people, too, and by sitting back and seeing them as people, you can open yourself up to a whole new world of beauty, seeing something that you created finally coming to bloom. It is the sweetest high a mother can ever experience, and it's worth every minute of the nail biting, teeth grinding work that it takes to switch those gears.
This beautiful young lady is on the verge of motherhood. I don't doubt that your husband went ballistic. His daughter wanted to get attention from him, and boy, did she get it! Now he's out of his mind, and she doesn't feel ignored! Teenage pregnancy is unfortunate, but it is uncommon, and though frustrating it's not the end of the world. A woman's body changes as she progresses in her pregnancy, and her moods change as well. I was an out of control teenager, but as I progressed in my pregnancy, I found that I had something that was truly mine, that I could love with all my heart and wouldn't leave me. It was an incredible change, realizing what was going on! Have you asked this girl how she feels about motherhood? She's going to be 18 soon. How does she feel about being an adult? My guess-she's scared to death-adulthood means no more dependency and a whole world of people lined up to ruin your day! Whether she is angry, sad, or just doesn't care, at least you know what you are dealing with and you can find answers from there.
As far as the ex-wife is concerned, your husband needs to remember that YOU are his wife, and quit playing the victim. He's letting this "other woman" run both your lives, and if you let it continue, it will tear your whole family apart. Talk to your husband. Tell him how you feel. Let him know that you love him very much but you feel like he is still married to his former wife, and you need to know that you come first. Don't say things like "I want" or "You should". Use words such as "I feel" and "I need" and "It's important to me". Let him know how much you care about the children, but he needs to set definite boundaries with this woman. Otherwise, things will only get worse until someone explodes from the pain. If the kids are supposed to be coming to visit, and she doesn't produce them, you take her to court, you call the police, whatever you legally need to do. Not only does she need to accept that she is not going to ruin your lives, but the children will ultimately appreciate it as well. It shows that at least one parent cares enough about them to make things right. If the daughter calls when she and mom are arguing, tell her that she needs to call back when they are done and hang up. You don't need to be part of their problems. Your focus is on the daughter, and how you can help her, and you're not going to do it by letting mom pull the strings.
Make sure the daughter knows that you are not trying to be her mom, but maybe you could get to know each other and be friends. She could most certainly use a strong authority figure right now. Don't criticize and do your very best to try not to react to anything she says. Traumatized people are terrified of intimacy, because that means a possibility of rejection, and that means pain. If she gets too abusive or uncomfortable, politely but firmly ask her to leave, and make sure she does it. If you are in public, then you leave, but only until you get yourself under control, then come back and continue the conversation. Go in the other room, scream and yell, cuss, curse, kick the wall, whatever you need to do, but always, ALWAYS be patient and calm when you talk to her. I promise you it will work in the long run. I had many, many people who were patient with me and it's one of the reasons I am the person I am today.
Most of all, take care of yourself. You are not responsible for these problems. You can't change what has happened in the past but you CAN change the future. Join a support group. Get professional help if you need to. By working on yourself you will force the people around you to react and act differently. Don't get so absorbed in the problems that you can't think straight. You have a tremendous amount of strength just by asking for help. That's why I am taking the time to do everything I can to help. Please, please update and let us know how things are doing. I'll be looking for your posts. Good luck! :)