Hiya,
I can't really say anything specific about eating disorders, but I can really relate very much to the other things you've described, and I can offer a bit of general advice too.
Firstly, it's natural that parents treat their kids differently. Nobody is born knowing how to be a parent - it's something you learn. Parents learn from their experience with their first child and treat their second child differently. Maybe yours were too slack at putting the foot down with your brother and then they overcompensated with you when they realised they hadn't been tough enough with your brother. The same thing happens with each subsequent child, and everyone with brothers and sisters goes through the same thing.
Anyway, I've also had problems coping with the things my parents could've done better. I'm 30 now and I've never really had a girlfriend and I've only slept with a couple of women. My Dad in particular is really excruciatingly shy and that's come out in me. Both my folks have also encouraged me to be interested in things (which is actually what produces high achievers in school), but never made me work hard and strive to make my position in life better (which is what produces high achievers at uni and in work). Seriously for years these things caused me upset and outright depression. Coming up to my birthday this year, I was even considering getting so wasted the night before that I wouldn't really wake up until the day after, even though these days I'm normally totally fine.
When I was 15 I started going out, and drinking was a big thing where I lived, but my parents hated it. My Mum told me the last time she could remember my Dad actually being drunk was in the mid-80s. Dad would go ballistic when he found me drunk and cue comments like, "You're ****ing up your life!" etc etc.
I know it's a struggle to deal with these feelings, but I think that it's important to differentiate between blame and responsibility. People make mistakes and as you get nearer my age you'll start to appreciate more and more and more how many of them your parents have made. But it's not a blame game. They're still your parents and they're probably doing their absolute best for you. Nobody's perfect.
The responsibility for dealing with these problems now lies with you, because adults deal with their own problems. That doesn't mean you have to do it on your own - just that it's your responsibility. If you can move yourself into a frame of mind where you concentrate on the responsibility and not the blame, you WILL start to move forward.
Try and put your thoughts into compartments, like you're packing old photos into boxes. You don't have to deal with everything at once, as long as you can keep at the back of your mind the worst feelings about what you're keeping for later. You don't have to have normal principles about dealing with mental health - you just find a way of processing your problems that works for you and then grab hold of that and go with it.
I hope this is a bit helpful. People can be different, but post back if you want to chat more.