Pennsylvania has subscribed to the Interstate Child Custody Jurisdiction Act, which is a law that provides a set procedure for determining which state may exercise jurisdiction in a custody case involving two or more interested states. The situation arises, for example, when one parent resides in this state and the other parent lives in another state. The issue of custody must be decided in the family law court of one of the two states.
A recent case involving two other states illustrates the process. A couple were living in a western state with their son, which led to the father's parents regularly watching and caring for the child. The parents returned to their original state in 2015 but they allowed the grandparents to care for the child periodically at the grandparents' home because the couple were having marital problems.
The father then returned to his state, Oklahoma. The wife remained with the child in Indiana, where she filed for divorce. The grandparents entered the Indiana case, seeking child custody. That court decided that it had jurisdiction under the interstate custody laws, and it ultimately awarded child custody to the mother.
The Court of Appeals in the mother's state recently affirmed that the family law court in that state had appropriate jurisdiction to issue the child custody order in favor of the mother. The appellate court approved the findings of the trial court to the effect that the mother was gainfully employed, with benefits, had clean drug tests, and generally showed a trend of progress in her life. The mother's progress in that respect would typically give her the edge in a custody dispute with the grandparents, whether it be interstate or within the same state. The case appears to have been decided correctly and would likely be approved by the courts in Pennsylvania, based generally on the mother having acted first and on her superior ties to the child in her state of residence.
Source: theindianalawyer, "Decision upheld in Oklahoma-Indiana custody dispute", Olivia Covington, Jan. 25, 2018