I bet it has been a long time since someone has told you that it is okay to love your husband/their father. But it is okay, in fact it should help make the situation better. JMHO (never been there). Also, always let your girls know it is okay for them to love their daddy. So many times, I have seen the children get pulled.
One of the boys that I call my own was legally raised by his grandmother because his mother was/is a drug addict. Every once in a while she would come back into his life and make all kinds of promises. We knew she would be gone before long and we would be the one to help him deal with the fresh hurt. But, whenever he would talk to me about her I would always tell him it was okay to love his mother. I really think he was comforted by that because what he mostly heard was how sorry she was (and really he knew/knows it) but he still loved her. I tried to explain and make him know that she was not doing this to him and that she loved him in her own way. The addiction was just too powerful. I told him many times to love her but hate her choices and never get caught up in that world. You know what, something was right because he is still a good kid (20 years old) and has never been in any trouble.
12 years old is a hard age in the best of circumstances. Therapy would probably help and be good for all of them. It can be really hard handling and watching them them go through this age. If it hasn't started yet you will see it, one day they want to be a kid and the next day they want to be a grown-up and then the next day they're back to being a kid. It is hard. Not only that, their bodies are physically changing and throwing them another curve. Just always keep this in the back of your mind - "those that need love the most, deserve it the least." When your girls get difficult and sassy (and I have faith they will), if you will run this through your mind, I promise your actions and reactions will change for the the better.
Well I've rambled enough. Just keep taking care of those girls. You will be rewarded in the long run with 2 well-adjusted young women.
Hope it was okay to talk about kids here. If not I can and will delete this.