How can a father get custody of his 4 year old child

4years old child's mother has ran away form the child's father and the child's maternal mother has been looking after the child for the last 3months. Child's father wants to take a full custody of the child and the mother has abandon the child and gone abroad but does not want to return to look after her child and wants her mother to take care of her child but the child has been neglected and malnourished and the maternal mother does not have sufficient accommodation facilities to bring up the child. Please advise the legal rights for the father who is financially in a better position to take care of his child and he is a loving father. Maternal grandmother refusing to hand over the child and the child also wants to go with her father. The maternal grandmother does not want to leave the child and planning to demand and get financial support from the father also refusing the child to spent some quality time with her father to look after the child, refusing phone calls as well.