Multiplayer will support the player amount, as long as it is modded in. That was part of a big question about the mod tools during the Reddit AMA. Of course, the dialogue is meant for just the 2 main characters - either you playing single player and controlling both, or playing multiplayer and you and a friend controlling one main character. A mod can add more player support for multiplayer, but they might need to change the dialogue around to make it sound like there are more then 2 people. Would be weird to have a mod with 4 players, and have text say something like 'And you 2 will be...'.
