Make sure that you hit all switches. There are several places in Kefka's tower where one group has to hit or stand on a switch for another group to be able to proceed. At the end you will need to have two of your groups standing on a switch on each side of the walkway to open the middle door. Then take the middle group up to push the weight off of the balcony onto each of the switches. Then you can continue with all three groups.