...........there were a total of 4 persons on the flightdeck
Were they all on the flight deck ? Do relief crew sit on the flight deck for take-off on this aircraft / Airline ? If so, are they part of the operating crew, which could impinge on their ultimate, eventual, duty hours available ?
If not part of the operating crew I wouldn't have expected them to have been involved in the take-off calculations, although from a self-preervation point of view I might have expected them to say something as the runway was slowly being eaten up before them with slow acceleration, even as a passenger down the back I time the take off roll, and have a mental point beyond which I might start to get worried !