Can I adopt my stepbrother and get some financial assistance?

My stepbrother came to live with me full-time after his dad was found guilty of abusing him. Our mom took the dad’s side and my stepbrother didn’t want to be around either one of them anymore. He’s 14 and I’m 23. My boyfriend and I are doing the best we can to take care of him and support him financially but it’s hard and we could use some help. Is there any way I could formally adopt my stepbrother and get some financial support for him from the state? Or could I take legal guardianship of him and seek child support from my mother and stepdad?