As long as you are identified as being the only one with a problem, family members don’t need to face their own responsibility for whatever happened, and it’s unlikely things will change. However, since some family members are supportive, a toehold already exists for making change. From my point of view, then, this is a family therapy case, not a situation that will be improved with individual treatment.
If you haven’t already, please talk to your therapist about expanding your treatment to include the whole family. If the whole group won’t come, start with the people who are allies. If your therapist doesn’t feel qualified to change the mode of therapy, ask for a referral to someone who has experience and expertise in working with the whole family in the room.
Meanwhile, writing is an excellent way to manage your own feelings. I hope you are sharing your writings with your therapist. You will also feel more empowered if you are doing everything you can to get ready to live on your own. That means doing well in school so you have a chance at scholarships to college and/or developing some job skills so you can leave home and support yourself
I wish you well.