By Jove, I Think She's Got It!
Check out this expert from Twinparenting.com. I think we'll all recognize that we suffer from TES.

Are you a victim of Twin Escalation Syndrome?
Twin Escalation Syndrome (TES) is the tendency for twins, triples, or more to feed upon each others behaviors, and to escalate the behaviors in reaction to each other. TES. If you are a parent of multiples, you’ve got it. Every day.
If one multiple gets scolded for bad behavior, the other(s) must immediately perform the same action that resulted in the scolding – and often build on the behavior – bigger, bolder, “badder”. If one screams, the others scream louder.
In fact, Twin Escalation Syndrome often results in behavior that is so over the top, we’re not just talking “double trouble”. You’ve got the bad behavior of one, added to the bad behavior of the other, and then intensified — exponentially. Sometimes it seems that every bad behavior of one is picked up and mimicked by the other(s).
Twin Escalation Syndrome (TES) is the tendency for twins, triples, or more to feed upon each others behaviors, and to escalate the behaviors in reaction to each other. TES. If you are a parent of multiples, you’ve got it. Every day.
If one multiple gets scolded for bad behavior, the other(s) must immediately perform the same action that resulted in the scolding – and often build on the behavior – bigger, bolder, “badder”. If one screams, the others scream louder.
In fact, Twin Escalation Syndrome often results in behavior that is so over the top, we’re not just talking “double trouble”. You’ve got the bad behavior of one, added to the bad behavior of the other, and then intensified — exponentially. Sometimes it seems that every bad behavior of one is picked up and mimicked by the other(s).