If a round ends with a hidden defense card and an identical attack card, the points are doubled.
No. To be able to play an Empress as attack, there must be one already played as defense, by any player. (except for the last (attack) card).
If an Empress is hidden in defense, the other Empress can’t be played as attack (except for the last (attack) card!)
NO, this rule applies only for 4 player game.
NO, you must end with an attack card (taken from your hand).
No. When you use a card from the mercenaries, that card must be played immediately (can’t be added to the hand).