I heard a lot of anger and hurt in your postings. It is okey to feel angry and hurt with your step-mother. I can see that you are concerned that being angry with your step-mother will hurt your step-father. You are not responsible for the decisions and emotions of others. I had some unresolved issues with childhood (resentment towards my parents). I shared them with T and wrote some notes to my parents. I never mailed the letters out. I just shared them with T as a way to express my feelings. I suspect that this idea might work for you too. I think I have managed to forgive my parents after this. I suspect that you would need to stay clear of them for a while until you have worked out some of your feelings with T. Then, you would be better able to deal with the situation.
I also hope that you find a way to spend some time with father without your step-mother. However, it sounds like she might not allow that. If so, then try to work out some of the emotions with T and try to spend time with the both of them. I don''t know if you have many other options: avoid them, live with the situation as it is, keep talking about it...
I hope you find a way to deal with all of this.