Tried it with two players and the camera seems to be centered around the middle of the 4 players, so you can't go very far before the two active players go offscreen. Maybe keep the same logic, but center the camera in the middle of the players that already moved ? Or have the screen split in vertical slices when the players are too far appart ?
Speaking of 4 players, how do you set up the computer so you can play with players 3 and 4 ?

Seems promising.