Can I get custody of my little brother?

I am about to turn 26 years old. I live in Tennessee and my family lives in Michigan. I have an 11 year old brother that my parents and other siblings "hate". They treat him horribly and wonder why he does the things he does, why he gets into trouble. They treat him horribly mentally and threaten him physically. He called me sobbing again today that he loved me and had to say good-bye to me... Because my mom was going to kill him, or make him pack up his things and drop him off on some deserted country road. While I was on the phone with him I heard them say nothing but absolutely DISGUSTING things to him! I moved out of my families house when I was 15 1/2 because of the HORRIBLE mental and physical abuse, but if you ask my mom she's done "nothing wrong, not my fault they act this way" but when you spend 18 hours a day on facebook playing farmville and you complain you can't control your kid, I WONDER WHY!!!??? I'm sorry to seem like I am shouting, but I know if I had not gotten out of that house when I did I was going to end up dead by my parents hands, or my own... What can i do to get him out of there? How do I go about petitioning for custody? I love my entire family, all of them, even my parents, and that took me a long time to say that. They claim that this behavior isn't "learned" but it is, when you have two unstable people that taught us all how to be unstable. Its taken me MANY years to get stable with work, and my mental issues. I don't want him to have to go thru all of the hell I went thru as a kid, and I want to "save" him before he gives up on himself. Plus a mother that threatens to kill, poison, choke, beat, and throw out on the street an 11 year old, means that he doesn't need to be in that situation. Was trying to get her to let him stay with me for a while but shes thick headed and won't listen to anyone, and just continues this "mental warfare" on everyone around her, but she's admitted to hating him, everyone says that they "hate" him. But I love him, I don't yell at him I give him respect and I've always gotten it back. Please someone help me I am sick with worry... I really fear for his life, livelihood mentally and physically.