I don’t have enough information to know if you are being “abused”. It does seem that your life is very complicated. You are a responsible and intelligent young man. A household of 8? I gather that there are other kids in the family, which already makes life complicated. And your mom and stepdad aren’t getting along. And you also recently moved. All this adds up to a high score on the stress-o-meter. It makes sense to me that you are feeling less than wonderful.
I suggest you do the best you can to minimize how much you need other people in the family to validate you. It sounds like they themselves are equally stressed. Instead, do what you think is right and best. Then focus on making new friends and connections in your new town. A part time job is one of the best ways to do that. Do the job well and you will also get some of that validation you are looking for. Your involvement with theatre is also a resource for both friendships and validation.
What will not help is staying home and in your room. Isolating may help you avoid some kinds of stress but it creates even more.
If you have difficulty getting motivated to do the things that will help you help yourself, I suggest you talk with the school counselor or find a therapist to provide you with some needed support. If you can’t do that due to cost or privacy issues, consider calling the Boys Town Hotline. Counselors are available 24/7 to talk to teen like you. It is free and confidential. Here’s the website: http://www.boystown.org You can call, chat online or write.
I wish you well.