My ex-husband adopted a girl who is now 9. he is very psychologically abusive. What, legally, can I do to help her?

We fostered her together until our divorce. My son was physically and mentally abused by this man. Now my dtr. is 19 and he is physically and verbally abusing her. I am afraid his pattern will turn on the little girl when she begins to have a mind of her own and make choices that dont suite him. My son is irreversably damaged by this man. The abuse on my dtr. started when she told him she was moving closer to me after she was getting married. I want to know if the little girl, who is also an american indian and on the tribal roll, could come legally live with me? or with her 19 yr old sister? please someone help give me an answer. She is a beautiful little girl and I do not want to see her living this way.