Basically, before the family left Cuba, the father would visit the children about twice a month while failing to notice any abuse by the mother. After she took the kids to the US there was no visitation, but the abuse continued. Eventually the abuse was noticed when the boy convinced his mom to call the police before she attempted suicide.
An American family has adopted the boy, and the girl in question has lived with them for 18 months. She calls them Mami and Papi, but there is a question on whether she should be returned to her biological father or remain with the family that has adopted her half brother. The family also wants to adopt her.
For me the answer is simple. He wasn't a huge part of her life before they left Cuba, or after. Let her stay with the family that loves her, and has cared for her the past 18 months. She will then be in an intact home with her brother.