It appeared to me that Holly was just beginning to realize last night that she was being used. It was good that Dave approched her. I think it will take some convincing to get Holly to change sides. If Melanie does not stay and Scott goes back to Holly, I don't think she will switch. She does not seem interested in playing the game just sticking with Scott and staying in Paradise. Now if by some miricle the good guys pick Melanie to stay then we have a new ball game. Holly will definitly want some sort of revenge.
While I think Scott is disgusted by the behavior of the children, he is there for himself. He is not going to speak out against anyone. Everyone needs to remember we do not know yet how this game is going to play out. No one knows how the voting will go or who will be involved in the voting.
Personally, I would like to see the producers leave it up to the public/fans of the show to vote who should win the "ultimate" prize.