You need four players, because you need two people to hold gates open, so two players let other two inside, and those two, when inside, open the gates for the first pair. No way around it.
You only need three to get through this wall - two open the door, one runs through. One of the door openers disengages and the person that ran through activates that side of the door from their side of the wall. Then the disengaged player runs through, and finally the two players on the far side of the wall open it for the remaining player.
Which is completely academic, since you do
need four real people for the final element of the heroic. One to throw the switch that lowers the forcefields. Two (one on each side) to use their Ghostbuster beams on the cores, and one to throw the grenade that destroys the cannon.