Sony confirmed that PlayStation Move cannot support 4 players in its full configuration.
The complete experience of PlayStation Move requires two controllers per person, either two PlayStation Move wands or one wand and one sub (nunchuk-like) controller.
This mean that four players can’t enjoy PlayStation Move titles at once. Each player can use a single Move controller, much like some Wii titles need only the Wiimote. For the full PlayStation Move experience, each player needs two PlayStation Moves and a sub-controller. The reason why you need two Moves AND a sub-controller is because the sub-controller doesn’t support motion gaming at all, and the Move doesn’t have that analog stick you find on the sub. Some games will require Move + sub, some will require two Moves. You also need one PlayStation Eye that services all four players.