I have a group vs group game working, the concept of which may work for you.
My game has 100 Civilian units, any of which can play solo free-for-all, or team up in groups.
Solo units are renegades with a rating of -9999, and group units perpetually get their rank set, forcing a rating of 0 while they're in a group of more than 1 player.
https://www.reddit.com/r/armadev/comments/109g4ma/i_cracked_the_code_for_group_vs_group_games/