The Rook is a special piece in superchess. This is because it is allowed to castle with a rook and King/Emperor or both. Yes indeed if you have King AND Emperor and two rooks, you can castle twice. You can only castle with the rook, not with any other of the non royal pieces.

This message and the preceeding are based on the book: "Schaak en Superschaak"by Henk van Haeringen, the creator of the game.