If I'm not in a safe environment, can I live with my aunt?

I'm a sixteen year old online student and I'm at home most of the time. I do not feel safe at home. I live with my mother and sister. My sister has mental problems. A week ago the police had to be called because she attacked me and pulled a knife out on me. She is twenty-one. I'm constantly worried about my life living here. My mom says she will send me to a youth home if I try to leave. She's threatening my freedom. I really want to live with my dad (in Chattanooga), but he has a disease and I can't stay in his hospice home. So, I want to live with my aunt. I lived with her when I was a baby-toddler due to my mom being in the Army. If I don't feel safe where I am know is it possible that she can gain custody of me? I am constantly being threatened, I have to defend myself physically and verbally, and the fact that my mother does not seem to care is an issue. A very serious matter happened with me when I was younger between my uncle and I and since then, she has not cared about me like a mother should. I just want to know if my aunt can get custody of me?