Ex changing custody at whim

my fiance and his ex were divorced in nc and have an unincorporated separation/settlement agreement that covers child custody. he is supposed to have 7 weeks with his kids in the summer and 2 weeks during winter break. this past summer, she decided that the kids could only come for 12 days, claiming the kids didn’t want to come at all, also stating that she couldn’t make them (the kids are 16 and 11). she moved them to maricopa county, az, with the kids 2 years ago. my question is this: to enforce the agreement, i understand he would have to file some sort of motion, which the courts would treat as a child custody motion. am i correct? also, would this have to be filed in az or could it be in nc courts? thanks in advance.

While technically, she is in breach of the custody agreement, his best approach would be to file suit for the court to determine custody. Jurisdiction would likely be in AZ since the children have resided there for 2 years.