That's pretty horrible to go thru, especially at a young age. Don't suppress those feelings, they may come thru in other ways. Obviously your stepmother was taking something out on you. The people that either joined in or did nothing are not blameless. They might of been scared of her or whatever but shame on them anyways.

I agree to look for a therapist and start reading about abuse survivors, PTSD, and forgiveness. I know that forgiveness looks like the last thing you want to do, I get it. A friend told me its the most selfish but best thing to do for yourself. She doesn't deserve to have the ability to torture you after all these years. You can stop her from hurting you, by getting help, getting better and living a awesome life. Good luck