Well, firstly, if a game has 9ppl and it's a 4v4 game, then anyone who has activated "find me a game" gets moved out if a game can be found. 9th player stays in if no game can be found among other ppl who have clicked "find me a game", do send a warning in this case.
Only one gets moved out (random among equal considerations, but elo matching will often favour one), the rest keep their game.
Exceptions:
9 ppl is odd and thus 1, 3 or 5 ppl (if so many have clicked "find a game") could be moved out to leave an even number behind. (note that 7 cannot be moved since that would turn it into 1v1)
Prefer to move as little ppl as possible. Movement should be disfavoured over game preferences.
If none have clicked "find a game", send a periodic warning in the chat that they have too many ppl and can't start. Let the players work out who should click "find a game" or maybe someone will spec.
Obviously, if someone sits in a small teams room without clicking "find a game", don't move him. But do move other people into that room if a small team game can be made with him.
If multiple unmovable people in separate small teams exist at equal considerations, then pick one randomly. (elo match will often favour one set over others)