I am with Gordy. Same here. Customer demands two engines and two pilots.
Any flight ops manual/SOP, especially in Europe, does or at least should have that situation covered and it will usually say: "In case two rated pilots are in the cockpit the chief pilot will designate a PIC in WRITING".
So there are no two opinios about it.
And the second man is not just in for a jolly ride, as stated, he has to earn his per diem by acting as a PNF, pilot not flying, navigating, radios, checking instruments and airpace. Keeping track of timing, fuel, etc. you get the idea.
He can of course take over in case the PIC becomes incapacitated, that's the idea behind it.
Now, of course, he can't log any pilot time, neither PIC nor SIC, but that's another story.
