An overlapping crush occurs when two people have highly similar characteristics and/or interests, and are liked by, or like, the same person.
Also occurs when two people are liked by one person and equally do not reciprocate those feelings.
William: Hey dude, you know that Rebecca likes me?
Louie: Dude, she likes me too!
William: What the hell?! But I don't even like her!
Louie: Dude, me either... Definitely not.
William: Holy crap!!! We have overlapping crushes!