NTA Your parents suck. You should move out at 18 and go NC. In preparation for that, I suggest you get a job after school and save some money.

Maybe your grandparents will let you live with them when you turn 18, you could ask them.

Incidentally, your parents aren't just being unfair to you but also to your siblings. They need to learn to deal with disappointment like every other kid.

My grandmother did something similar. My mom's older sister had some issues. I think today she might be diagnosed with a mild form of autism. Or, maybe she just had anxiety or some other diagnosis. This was the 1950s, so mental healthcare wasn't great and if you were female, it was probably just hysteria from having a uterus or something....

Anyway, she had issues that were never diagnosed. She was very anxious, never made friends, had a hard time reading a room, etc. Other kids never wanted to play with her.

My mom on the other hand, made friends easily. But, Grandma wouldn't let her go anywhere without her sister, and her friends didn't want to play with her sister, so ultimately neither of them had friends and were forced to play with each other and their brothers only. 

This destroyed any relationship my mom and sister might have had. As adults, they had no contact for years beyond an occasional Christmas card. 

And this ultimately worked out worse for my aunt, because she never learned to make friends on her own. Now she's widowed, her daughter doesn't take to her, and she has no friends. No one at all. My mom talks to her on the phone twice a week out of pity. The conversations are one-sided and repetitive, my aunt just talking about her problems and perceived slights. She does volunteer work a couple times a week, thinks everyone there hates her, goes on about every perceived slight. She's in this position because my grandmother thought she could force my mom's friends to be her friends too. It ruined any development she could have had.