If multiple sources would deal damage to the equipped creature at once (for example, several blocking creatures), 2 damage from each of those sources is prevented.

If a creature is equipped with two Shields of the Realm, 4 damage will be prevented. Three Shields of the Realm will prevent 6 damage, and so on.

If multiple replacement effects would modify how damage would be dealt, the controller of the permanent being dealt damage chooses the order in which to apply those effects.