Can my MIL refuse to return my children based on POA?

In 2009 we signed a POA for the care of minor children and sent kids to temporarily live with Grandma. At the time of signing she attached "termination criteria". We have met all of the agreements except obtaining my drivers license and based on this she is refusing to return the kids. My questions are first, does the "Termination Criteria" trump my ability to revoke at any time even prior to a stated ending date (as stated by NC law). Secondly, can she use the POA to file for custody under abandonment without our knowledge since she has been caring for the kids for more than 6 months. She is not above claiming inability to contact us for consent to custody. The POA form was a legal doc purchased online, the termination criteria was hand typed but was notarized with POA.