Just read the update. Wow. Seems your parents have just accepted this as normal. I honestly can't comprehend that. Wow. Like others have said, get out of there. If your parents aren't even going to acknowledge the problem... damn. And I thought my family was fucked. At least my mom and sister acknowledge our problems...
For what it's worth, I've been seeing a therapist for the last couple of years. I don't know the details of your treatment, and there are several generic types of psychotherapy and it's all ridiculously individualized; but I can speak from experience that trying to blot out the memories won't help. Doesn't mean you have to remember them on a regular basis, but as you improve and get on with your own life they'll fade. You won't think about them as much, but they never, at least for me, get any less painful when I do remember them; and no matter how much I used to try to suppress them they never went away. Granted I haven't allowed things to get as bad as your place, at least physically; and you're a female so you're naturally wired differently than me. Just trying to help.
To be honest, the only reason I'm sticking around at all (a few weeks a year) is to protect my mom (mainly by reinforcing my presence, although I'm ready to follow through if I have to). For a number of complicated reasons she's incapable of leaving my dad. If she did she'd go bankrupt in 3 years from medical treatment alone. Let alone the other reasons. Point being, if I could somehow get my mom free of the bastard I'd cut off contact even with her. My mom is locked in by her problems, and I'm in turn locked in by my values. Hell I still don't know what I'm going to do when I graduate (I'm 21 by the way). You have a way out, your parents have a way out, and hell even your brother would have a way out if he got off his ass; and from the sound of it there's not much if anything you can do. Get out of there. It'll be painful as hell initially, but it'll do you a world of good. Literally. :thumbsup: