It seems your parents' AP applications were rejected. If so, they can not leave US before the new AP applciaiton is approved, otherwise their I-485 will be denied. AP does not need fingerprinting. Also, fingpringting only can be done within US, if any. You also can not stay in China for more than one year continuously unless you have the reentry permit which allows you to stay outside US for > 1 year < 2 years.