How do you copy animations?

Okay, so I am new to Character Animator, and I have a pair of characters that are twins. They have two separate models and the only difference between the two of them is their hairstyles. I am trying to get them both to flap their arms bird flapping style for a music video I am working on. Is there anyway that you can take a recorded animation of one arm flapping and apply it too the other arm? I need them to be flapping in unison and I need them to be doing it at the same time. Any help would be great! Cheers!