Even on the 747-400 on flights that exceed 14 which are quite a few,you need two complete crews. Different airlines comply with the rule differently.
Some airlines use 2 Captains. Some Use one Captain and 3 First Officers. I believe tht one would have to be type rated to do this. United type rated everybody in this long range crew for that purpose even though many times people did not get takeoffs and landings. The number of legs per month can be as few as 6 in a normal month often split by a Captain and First Officer.
Still other airlines use a relief pilot or cruise captain that is training to function as Captain from cruise and is usually only able to takeoff and land from the right seat.
Some airlines use Second Officers(not to be confused with a flight engineer which is not to be confused with an engineer in some parts of the world is a mechanic) who are ONLY qualified at cruise or once the airplane is airborne.
Either way, you are tired at the end of the trip!