When multiple players declare coronation ceremonies, the game goes into sudden death overtime. When this happens, players who didn’t declare coronation ceremonies are out of the game, and skip their turns. (Eliminated players are not affected by attack cards.) During overtime, the first player to reach 30 or more Succession Points puts their princess on the throne and wins the game.
Once overtime begins, you still continue playing even if the total of Succession Points in your Domain drops below 20.