Could I give my dad custody?

I'm 15 (almost 16) and I live with my mom, brother (30 yrs old) and his daughter (10 yrs old). My mom & I constantly fight, she always makes me watch my brothers daughter and says it's my "responsibility", when she's not my child for me to be watching. I've spent most of my summer watching her, and I've finally got to my breaking point. My mom wants me to pay things for her, but I can't get a job or she'll lose my SSI, my mom wants me to watch my sister, but I have another under the table babysitting job that I have to attend to, she wants me to do everything I shouldn't be worried about at this age.

So, I want to give my dad custody. He's a good person, he's an alcoholic but not the mean type. He has a place for me to stay, and he wouldn't make me watch any of his kids, basically because I'm his youngest. I'd be able to go to the school I WANT to go to, without hearing my mom rant about it. I don't know how to do it, but I know that I want to.

I've heard of kids getting to choose who they live with, but could I do that too? They're separated, but not divorced. His girlfriend treats me more like a daughter than my own mom does.