Shield of the Realm

• WOTC Official Reminder Textofficial rules
  Equip — Equip [cost] ([cost]: Attach to target creature you control. Equip only as a sorcery.)

• WWizards of the Coast2018-04-27
  Official Ruling
  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.
• WWizards of the Coast2018-04-27
  Official Ruling
  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.
• WWizards of the Coast2018-04-27
  Official Ruling
  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.

Rulings via Scryfall