I browsed for this but didn't find the definitive answer- The way we have been playing is that the player who is the turn player has the shadow card dealt the enemy engaged to everyone, and once they have resolved blocks, the next player is dealt a shadow card when it comes to their turn to resolve blocks, and so on. This seems more graceful than dealing three shadow cards for the enemy and resolving them as you go around. Would love to know the technically correct answer though.

[2019 ruling]

Ah so looks like this was played correctly, unless I do not deal the initial shadow card to the first player? Not that it would usually even be relevant but there are situations it could be.