ManaAdaSystem -
One captain and two copilots. I put my money on this being a training flight with a new F/O.
I guess you've seen and heard the recorders already then, right?
I can see it being the Line Captain getting his 25 observed hours in. I can see it a Co-Pilot getting checked. I can see it the Line Captain getting a route check or line check. Maybe it was just a Jujmp Seat rider who wanted to observe. Maybe it was the equivilent of an Air Carrier Inspector. Any number of possibilities for that third person.