How are you moving them atm?
I'd imagine having a front and back battle spot, and a variable set for which member is front or back set with a "switch" action-ability to use a battle event to switch between the two should work.
IE if they are battle spot 1 and there are 3 front and 3 back spots, then theyd move position to battle spot, lets say 4 (the back position of 1)