Oh, Ky, TN

I am asking for advice for a friend:

4 year old in custody of maternal grandmother because childs mother neglected him, domestic violence, and drug use. Father is fighting for custody and up till lately grandma refused visits. Judge granted him one week a month in home visitation and now grandmother is having a fit. He picked kid up last sunday and as soon as the kid got in the car he told his dad that if he punished him he was going to call 911 and his grandma told him to. Then he told him that grandma took pics of him naked with her cell phone and is planning on telling law enforcement dad abused him. What can he do about this?