“When the size of the party is equal to or less than the team size, the party will be guaranteed to be placed on the same team”
I read that as “team size” as the actual number of players currently on a team, but it looks like they mean the Team Size setting.
I guess my only option is to give the players the ability to change teams through a teleporter in their team base or something similar. I don’t see any code methods to check player’s squad associations.