Gaining Parental Custody of 13 year old daughter?

Our 13 year old grand daughter in NH wishes to live full time with her father and stepmother. My son who also lives in NH does not have the financial resources to go to court, but wants his daughter to live with him also. What are the options to get this process done. The Natural mother is just short of mentally abusing our grand daughter. We have told out grand daughter to talk to her Guidence councilor and maybe the state will step in, but we are only guessing on that. Any lawyers, or folks with legal background that could give us some advise. Thank You.