Someone asked a very good question and I should clarify this: 

If you are in a team, only one member of the team can join the jam, and only one can summit the game and rate other games. However, all members of a team can decide the rating of a single game. This is to prevent, unfair situations, please be a good sport.

Btw, everyone in the team will get the role "game jam winner" if their team wins.