Originally Posted by
LHR/MEL/Europe FF
even if you reserve two tickets, a passenger cannot hold two seats on one plane unless special arrangements have been made (for example extra seat for personal space) one of the two reservations will be cancelled as a duplicate.
if it got that far unnoticed, the passenger will not be able to board with two tickets.
I think the ops question is more about having two reservations under the same name at the same time rather than flying with two tickets