:( Megan, from what you tell about your parents, they sound really cruel and unempathetic. They they seem to not accept your feelings, to even not allow you certain feelings, outright. Wow... There is little that's more hurtful to a person than having their feelings denied and ridiculed.
I actually feel like they are a lot sicker than you are. Seriously, who treats their own child like that? My parents were exactly the same when it came to my emotional pain. It got better when I moved out and it's so good to have people who just let you feel the way you feel, take your words seriously and are there with you.
I'm not sure I completely understand the legal position you're in. Were any of your rights transferred to your parents, like medical choices etc? If yes, you have the right to demand that you get someone else to make those decisions for you. There are housing projects for people with disabilities.
Regardless of that, please try to get help. Start by going to a crisis center, for example. Those people will first and foremost listen to you and accept your feelings (unless they totally suck at their job) also, they can inform you about ways to get out of you parent's house, away from their destructive influence, away from your dipshit brother.
You deserve to get out of there.