Board Thread:WARNING ALL USERS False Info\Spoilers/@comment-108.81.117.0-20130809225143/@comment-11533671-20130810043912

Ok....The Twins didn't learn to merge until Deucalion taught them and only after they were able to master doing this did they turn on their pack and eventually kill their Alpha.

"Ethan says they were the Omegas within a pack of brutal werewolves when Deucalion helped them develop their ability to merge together into a larger form. Once they'd mastered the ability, they killed the rest of their pack and joined the Alpha Pack."

http://teenwolf.wikia.com/wiki/The_Alpha_Twins