Grandparent wants a deeper relationship with trans teen

DEAR ABBY: I was recently informed that my teenage granddaughter is identifying as a boy. She has a male name she prefers and wants people to refer to her using he/him pronouns. Her parents are supportive, to a point. Her mother uses her preferred name and pronouns. Her father supports her using this name and pronouns in school and elsewhere, but at home, he will still use her birth name and pronouns. He has apparently told her this, and she accepts the situation.