If I am to try to figure out what you're stating, you seem to be saying that dad is accused of and being prosecuted for sexually molesting his fourteen-year-old daughter. The father has an adult child from another relationship who believes that her father is innocent and thus took it upon herself to harass the fourteen-year-old child's mother. This harassment was sufficiently severe that it was raised as an issue by the prosecutor at a hearing on dad's criminal case, resulting in the judge warning the adult child that if she continued her conduct she could be prosecuted for harassment.
Meanwhile, although the adult child does not want to report the mother of the fourteen-year-old child for having an unsafe household, and although at twenty years old she already has two children of her own, and although she does not believe the fourteen-year-old's allegations, and even though she has harassed the fourteen-year-old's mother, the adult child wants to somehow get custody of the fourteen-year-old. That's not going to happen.
There's no "retaliation" in having somebody prosecuted for harassing you.
Protective services has already become involved in the case due to the allegations against the father, and the criminal charges that the father now faces. It's difficult to believe that they have not visited the mother's home. If the extended family believes that the mother's home is unsafe, they may make confidential reports to protective services. It's not clear what the child's mother has ever done or could do to "retaliate" for a confidential report to CPS -- the only harassment that you describe was committed by the 20-year-old adult child.

