Can i give a Power of Attorney to a Family member to act on my behalf in a child custody case in Pennsylvania as I'm in Florida?

A family member is not allowed to represent you in court unless the family member is an attorney admitted to practice law in PA.

No, you can have a lawyer licensed to practice in Pennsylvania represent your interest in Court and the attorney can petition the Court in advance of the hearing date to try to obtain permission for you to participate and testify by telephone during the proceeding however proceeding that was is difficult since you cannot communicate privately with your attorney and it makes document presentation very difficult since you would not be able to view documents and discuss them with your attorney placing you and your case at a disadvantage.