They can indeed! You can play solo, 2 player, 3 player, or 4 player games.. and you choose whether you play against AI or other players (friends or randoms).

so can you play together versus ai? or is it a free for all?

It is pvp free for all. There isn't really co-up unless you both play the same player and help each other. There is some mild diplomacy or targeting the player in the lead.