That's true now that I look at it more closely to check that I had not missed anything. At first I thought that (expressed in terms of just two of the players) 1PN3 NxP 2RPxN RxR would cover it, making the danger to left Rooks ultimately dangerous for right Rooks, but I had overlooked 2 BPxN, which does indeed leave the left Rook unable to escape. How about the following? Both Castlings would take place the same side of the King, depending whether the inner Rook was still there.
Both Castlings would take place the same side of the King, depending whether the inner Rook was still there.