I hope you guys can help me, as I can't find the answer anywhere.

I set up a multiplayer game, but three players have not accepted or declined yet. What will happen to them if I start the game before they do:
- They become AI
- They won't join (meaning it'll become a 10 vs 7 game)
- Something else

I'm 100% sure they won't become AI.
It's either 10vs7 or it won't allow you to start game. But most likely it's 10vs7 (also automatically change this game to practice)

I started it, and it warned me about auto-booting the players that didn't accept yet, so I have my answer: Starting a game where not all players have accepted will boot the ones that haven't declined either.

it hsould not boot them, it should just remove them from the game like you do if you manually want to put out players you don't want in your game

Why would you start an unfair team game?

unfair games won't count for points so it doesn't really matter in that fact although boots still count towards your stats