To me it looks like B/C and J/T are on opposite sides of the room, whereas N/K may be the ones who've already completed the task- thus the empty iPad.
However it could go either way... maybe N/K or J/T are behind B/C. However, the footage of B/C does come across as them being slightly defeated. They look deflated, while the others look stressed and on-game.
I still think that N/K break ahead before the bungee jump, a lead they maintain to the final memory challenge. They finish the final challenge before B/C even arrive, leaving J/T and B/C to battle it out for second.
I think that if it were a tight race to the end, they would have played on that for the trailer. The fact that no two teams are really seen together suggests that there is in fact a bit of a gap between teams.
I think N/K have this. All signs point to their victory. They look excited and smiling in what appears to be the final cab ride, while B/C, only minutes from the finish line, look highly anxious and defeated.
J/T are a bit of a loose cannon though... however I highly doubt they will win with the extreme emphasis on both F/F teams.