How does multiplayer work in Divinity Original Sin?

They say the game is "multiplayer coop". But how does the cooperation work, in details? And how many players can play the same game? I've read it can be played only by two players but it seems a bit reductive to me, I would hope it could be played by a full party (4 people or more).

Thanks in advance for any replay.

EDIT: to anyone interested, here's the link to the 4players mod: http://www.larian.com/forums/ubbthreads.php?ubb=showflat&Number=504225

Solution 1:

There are only 2 people allowed. The host of the game controls one of the two main characters, the second player has control over the second main (wow- surprise, isn't it). So basically, host invites the other player (also possible while creating characters) and afterwards saves/loads the game, assigns additional 2 characters among players. Note that the player who joined the game is not allowed to play as long original host didn't invite them.

Solution 2:

Also worth noting (which is actually a result of the correct awnser) is when you are the host and you save a game, which you load later on, the player that joined you earlier, doesn't have to be in the game when you want to continue. The character he or she occupied in your game will become AI again, until he or she will be invited again by you to join.