Not quite - the co-pilots are qualified to sit in the Captain's seat in the cruise, so in the three pilot case the relief co-pilot rotates between his/her rest, the Captains seat and the Co-pilot's seat. The idea being everyone gets a break of roughly the same length. Ultimately if you've got the timing and sequencing right the 2 pilots who did the takeoff should end up in the front two seats for the landing
In addition Normal procedure in our Company is that the Co-pilot who was in the seat for take-off and landing outbound does the relief co-pilot job on the way home...