It's been forever since this has come up, officially or otherwise, but the last official word we got was that you can cap the bot numbers, you can set 0 bots and have player only, you can set the bots to balance teams at 3 vs. 3, then invite 2 friends, if they both choose your side it's 3 vs, 3 co-op, if they both choose the other team it's you and 2 bots vs. them and 1 bot.
Speaking of bots, are the bots called things like P1 P2 or do they have names? I saw someone called Molloy in a gameplay video, but I'm not sure if that was a player or a bot.