Five charictors at once... That sounds a lot like multiplayer to me
... But I suposs they may not all be used in every level...Like only the ones that happen to be near the main charictor at the time or something.
Or maybe when you start the game you get the choice of one other charictor to help the main guy for that game along.
Maybe in future single and multiplayer games you could chose which charictor you wanted to be at the begining of the game and follow there story... Some times iderpendent from the main charictors story, but still everyones path overlaps.
I suposs it all depends on how OWI would like to tell their story.