Have the Paladin’s two Armour ability cards face up and flip each one over when the player controlling the Paladin chooses to nullify the Overseer’s shots. The two Armour ability cards refresh in the next Setup phase, as normal. Playing this way avoids the potential issue of having to spend an action to activate the ability card. And yes it is the same for the Ethereal Amulet too. Semplara’s Amulet is always active as it is a permanent item and protects the hero from melee and missile with the fear modifier shots.
The Skeleton Hand functions in the same fashion as the Paladin’s Imperial Armour ability cards. They are used once per room and are flipped over after nullifying one of the shot types and/or modifiers in the nullifies box on the cards. The Orc Hide Shield also reflects one point of damage back at the attacker.