Love Letter Kanai

Yes. If you ever have the Countess and either the King or Prince in your hand you must discard the Countess, and you do not have to reveal the other card (page 8).

Yes — discarding the Princess knocks you out of the round immediately. If the Princess was discarded by a card effect, any remaining effects of that card do not apply (for example you do not draw from the Prince), although effects tied to being knocked out (such as Constable) still occur (pages 8, 11).

When you discard the Handmaid you are immune to the effects of other players’ cards until the start of your next turn; if a card effect requires you to choose a player but all other players are protected, you must choose yourself (pages 9, 5).

You cannot name '1' with the Guard — you must name a number other than 1; if the chosen player cannot be legally targeted (for example because of Handmaid protection), the Guard is discarded without effect (page 10; see Choosing a Player on page 5).

If the deck is empty at the end of a turn all remaining players reveal their hands and the highest-numbered card wins the round; ties are resolved by adding the values in each tied player's discard pile and the highest total wins, and if still tied all tied players win the round (page 6).

No — when a player is knocked out they discard the card in their hand face up but do not apply that card’s effect, and they take no more turns for the round (page 5).