(I hit "agree" instead of "respond", sorry for that)
I had very similar experiences. That makes you and me "brothers in arms". :-)
(Interestingly enough, you will find that many smart and successfull people's biographies read in a similar way.)
First of all - you are your parent's responsibility. From the moment you are born until you are mature enough to take care of yourself, their first responsibility is to love you, support you, and make sure you grow into a healthy self-sufficient individual. From what you write, it's safe to say that your mom, dad, and stepfather all failed in that respect.
Which means that - NO IT IS NOT ALL YOU, and NO, IT IS NOT YOUR FAULT. However, never underestimate how hard they will try to make you think it is all your fault. They would rather die then admit their mistakes. Unfortunately, that's how most of the people are. Try to understand that there people in this world who accept responsibility and those who don't. They are in this second category which is already crowded...
You are a sensitive person - something others in your household are not. This most likely means that you are more inteligent, intuitive, caring, and probably even better looking (unless your anorexia is really bad) then your mom or sister. This is enough to make them jealous. Jealousy towards one's kids and siblings is actually very common, only it's sad when it's parents feeling it.
The person who is smarter and better as a person will always attract jealousy from others, especially from family if they are not as developed. It's a simple (and ugly) fact. Try to accept that - some people haven't really advanced much further then monkeys. They walk and talk, and that's where their dissimilarities from monkeys end. That makes them dangerous to be around, and also makes us understand them better.
Everything you noticed about your mother, sister, stepfather and father is right on, which is actually quite surprising someone so young and who grew up in such tough circumstances. You are showing maturity of a much older person for a 19 year old (I actually kept forgetting you were only 19 while reading your message!).
One of the toughest things to accept in a life like you have right now, is that our parents maybe don't love us; and it's even harder to realize that they may actually hate us. Yes, this is possible. However, you were not born just by accident - you may not agree with me, but try to accept this: every one of us is on this planet because God wanted us here. Whatever your version of God is - nature, universe, highest love and power - well that energy needs you on this planet. Parents may choose to do God's bidding and help you grow, or they may choose to walk the path of evil, and try to distroy their own kids. Parents are free to do as they will - this is a planet of free will; everyone is allowed to do as they please. However, what everyone forgets is - we all do have to pay for our wrongdoings later... sometimes even before we die. And why are people allowed to make such stupid mistakes like abuse their own kids? Because, if there was a system to prevent it, God would never had a chance to get to know us. Some of us then advance further, while some others have "some 'splainin' to do"... And unfortunately, advancement always comes with equal amount of suffering. "That which didn't kill me, made me stronger" (Nietzche)
This way, we are all free to show what we are made of.
And you are made of some special totaly lovable material. :-)
What should you do?
There is no right answer. There are many possibilities. First of all, maybe the only thing you "Should" do, is realize that you probably don't see all of those possibilities. I am certain that some good options that exist, you don't see. And it is important to see as many possibilities as you can.
For instance - do you have any other relatives? Anyone who really loves you? Grandma? Uncle? Aunt? Is there a friend with whom you could share a room or something while you finish your studies?
Why am I asking all this? Because the only thing I would recommend in regards to your family is to walk out and never see them again. Never. You may disagree, but since you asked for an opinion, I feel free with giving it, even if it sounds radical. Do they love you? No. They are even kicking you out, right? Therefore, they want you out of their lives (even though they may say exact opposite at some later time, only to get close enough to you to hurt you again). So they are just simply evil towards you, and should best be avoided. It's what many call - poisonous people - they poison your life, and nothing good will ever come from them; even if something good comes from them, it will quickly be erased by something much worse. So in the end you come to this same conclusion - best to be avoided forever.
Then, you need to figure a way to support yourself. I don't know if you feel like you are mature enough to work, and take care of yourself, but you certainly seem very mature and smart to me; at least much more so then an average 19 yr old. Do you think you could get a job, any job, or maybe a job that you like, and pay some cheap rental with it? Or would you rather try to live with your father? If you are going to stay with him, my sugggestion is this - expect only the best from him, and the first time he tries to be abusive, even if it's only verbal, just walk out and never see him again either.
You mention a friend who offered help. This sounds great. I don't know if maybe you can offer to them to participate in their expenses and stay longer? Could you also maybe ask for some help from social services? Understand that you are just starting out and that asking for help is nothing bad - you need help, and you'll do whatever it takes to get it. This is so that you don't have to depend on people who use that against you (your parents). Just make sure you never ever ask for help someone you don't know (except government agency), or someone who is abusive towards you, or trying to put you down in some way. You have a right to live happy life on this planet, and people have to treat you with respect. If they don't want to treat you with respect, they can go their way - you don't owe them anything. You don't owe your parents anything either; they owe you though.
Once you figure a way to cover your expenses during your studies, you can finish the university and then get your career going. Maybe there is someone at the university you can consult with regarding all this? Maybe you can get a job at school where you study? You may also need some therapy later, as abusive relationships with parents usually leave negative impressions... the biggest danger being that one day when you become mom, you may be abusive in some way toward your kids, or you may be afraid of starting a family, or may run into a wrong guy every time you fall in love... to help yourself, try to observe people around you and recognize those who are "good people" - just as a model to follow, or something to enjoy as a break from those ugly memories.
Starting out on your own won't be easy. But it will make you a stronger person, and above all - you won't have to deal with other people's crap any more. And that's worth gold. Also, once you are on your own, make sure that you find ways to fill your life with something that you enjoy and do just for fun - no other reason, but simply because you enjoy doing it. Maybe it's watching a film, maybe it's reading a book, or taking a walk; but try not to indulge in un-natural addictive things like shopping.
Also, do have a friend you can talk to. At least one. Tell the friend that you really appreciate their help and/or attention. It is important not to feel alone; here at curezone you may also get some support, but this is also all in cyberspace so we can't really give you a hug or be there when you need us...
So to sum it up:
- Stay away from abusive people, which means getting away from your mother and sister (and stepfather, and even father if he is abusive towards you). You don't owe them anything and don't have to see them ever again.
- Try to become independent if at all possible. If because of that you have problems at school, do talk to someone there who cares, secretary, your favorite teacher or whoever, and tell them honestly about your problems; don't sound whiny, rather tell them that you need this much time, or whatever else to get back on track.
- Try to get as much support from others as possible. Friends, other family members, etc. It is not a shame to ask for help when one needs it. Never think that you're really alone in this world. You've heard about the saying "Nock, and it shall open, ask and it shall be given".
- If you believe in God (or even if you don't!), say a prayer for yourself - ask God for guidance and for helpfull people. Watch the miracle happen. Whenever we ask for something from the bottom of our heart, we will get it - as long as it is possible and not something bad like revenge. A prayer won't hurt in any way, so even if you don't believe in anything, try it - who knows... Just remember you cannot change others through prayer - you can only ask for things for yourself. You can ask for other to be happy and so on, but that's very hard to get, as it also depends on their free will.
p.s. As for your anorexia, try to have a meal, even if it's just an apple, every three hours minimum. Never go without food for longer then that. And as you become more and more independent, you will slowly get better believe me. Your anorexia is just an influence from your family - as soon as they are out of your life, anorexia will slowly dissappear.
p.p.s. Because of all the stress you are under, I recommend, or rather - I URGE you to take vitamin B complex and vitamin C as well and vitamin E. You are maybe already taking these, but if you are not, they are really important to help you stay healthy during these tough times.
p.p.p.s. One day you'll be happy, you'll have your own family, and all this will be behind... and promise yourself that you will love your kids, will take them seriously, will hear their complaints, and above all - you'll choose a decent person for husband, a guy who will adore you and respect you!