If I have two Guardian Angel in a unit and enemy kill the unit, do I lose both?

No, you do not lose both. If a unit has two Guardian Angel gears equipped and that unit would die, only one Guardian Angel is destroyed.

According to RiftJudge FAQ #1622 and FAQ #8749:

  • Replacement Effect: Guardian Angel functions as a replacement effect. When the unit would die, the effect replaces that "death" event with "kill this Guardian Angel instead."
  • Single Application: Because the death event is replaced and prevented, the unit is healed, exhausted, and recalled to your base. Since the unit never actually "dies," the second Guardian Angel's trigger condition is never met.
  • Controller Choice: If you have multiple replacement effects that could apply to the same event, you, as the controller, choose which one to apply. Once that effect resolves and prevents the death, the other Guardian Angel remains attached to the unit in your base.

This interaction is consistent with the rule that you can only replace the same death event once.