I wouldn't be making all the changes at once. You need to do this all in two or three parts.
Firstly i'd be dealing with one brother at a time or both if you can handle it. As someone else said, give them a warning in advance and telling them you will be pulling the plug in 3 months time regarding the car, phone and anything else you have set up for them. They are big boys, they can handle it. Don't give them any choices. Even if they say they wont ever speak to you again, don't worry overly as they aren't really doing you any favours at all. They aren't and haven't been acting like family. Totally strangers would treat you better than they are.
As for your mother, don't even worry about what she has to say about your brothers. It will be a 7 day wonder and will blow over in time. Actually, you can tell your mother that the money you save on not having to bail out your brothers you can put partly towards your parent's medical expenses or buy her a new bracelet.
I'm sure your dad can see the whole situation, everything, you, your brothers, your mother, everything!! I'm sure he feels for you and i'm sure you could form an aliance with him. That's what i'd be doing. My own mother sends me bonkers at times and i never thought my dad saw the situation and her and how it all really was, but he did, he only never said anything. Then when i went through my divorce, bit by bit he opened up about his own frustrations, but i had to get the ball rolling first. Now we have a great father, daughter relationship and i think he's glad he did open up. So why don't you make the first move and i'm sure it would be like a ray of sunshine in his life and in yours.
As for your mum, that's a tough one!! I'd leave her for last and work away at her in tiny doses. By this stage you would have your brothers out of your hair and hopefully a friendship/aliance with your father. My own father sticks up for me now when my mother says certain things, he wouldn't have done this before. It's kind of put my mother in her place and made her realise and learn a bit more.
Not that i'm condoning your mother's actions and her upbringing of you, but you just dont know what type of life she had with her own parents. She most likely realised too late that your dad wasn't the man for her or who knows what occured early on in their marriage. There are just too many question marks. I've learnt this from my own parents, they realised too late that they were like chalk and cheese. My mother had issues from her upbringing which she tried to carry over onto me.
The fact is, you may never change your mother, but if you can make the other changes it can improve your life dramatically. You do need a support base outside of home, friends of your own. You also need to show some courage with your mother. Don't allow her to brow beat you or take you away from friends or hobbies. She is fortunate you allowed her to live with you. So like someone said, join a church group or some other group where you can make friends and acquaintences so that you have more and more things to take you away from home.
Best wishes and hoping things get better for you