This gets interesting!
Notwithstanding the different oppinions on how to integrate the augmenting crew, it will run down to whether a misinput will be determined as fault, and subsequently HOW the enquiring bodies will define the role of the second set of crew. Will they have any mention of beeing in the slightest way implicated and therefore blamed not having helped to pick up the mistake? Or will the active crew make any statement as to any distraction by too many people in the cockpit?
If an augmenting crew will in any way be held co-responsable, what will be the definition as per when their participation starts? Once they are in the cockpit? Once on board, as their time is logged as well?
If so, then the forcing of them beeing on the deck (by not providing seats) will be very delicate. In my former company they had seats and it was the active crew who would allow or disallow, or ask them to be present, the augmenting guys able to deny.
By forcing them to attend and if they will in any way be held responsible, a subsequent question will be: What happens enroute, when they are sequestred in the rearside topedo tube? If the signing skipper is there and unable to regain his seat in case of a emergency, will he be also implicated in any verdict?
The report and verdict of the concerned authorities will be very, very interesting. It might have huge implications on future SOPs, even hardware solutions ....