More my own personal theory coupled along with the comments from Marissa about the final 3. If the white room is the same as 2007 in the UK, two people will stay in there until one of them hits the buzzer in order to win a cash prize (50k) but along with this they must also leave the competition, the person who doesn't take the money gets automatic entry into the finale. This is where I think Sarah and Kieran are the ones to get put in, Sarah takes the money, and to couple with Marissa's comments, Kieran goes to the finale. While these two are locked in that room for a long period of time, the power couples compete in the water challenge for probably nomination. Could be completely wrong but it doesn't sound too far fetched.