During a line check the guy in the front left seat is in command. Full stop. Should the guy on the jump seat feel the need to interfere he must have reasons which stand in court. If you "blew it" let him help, if not..... I would not hesitate to offer a guy who interferes for trivia to either stay at the next destination or take over and fly the aircraft home. He won´t visit you in jail should his ideas proved to be wrong! The question which licence we where using on that particular flight helped to avoid any confusion of who is in charge so far....