Used to do that years ago on CL44s that could fly for 18hrs. A 'heavy'crew consisted of 1 Capt (there can only be one captain!) 2 FOs and 2PFEs , plus generally a nav and a loadmaster. Accomodation was two large bunks and a treble seat in the area behind the flight deck. It was possible to get a good few hours sleep, lulled by the drone of the props, and wake refreshed to get back in the seat for an approach and landing.