Board Thread:WARNING ALL USERS False Info\Spoilers/@comment-108.81.117.0-20130922203715/@comment-1587802-20130922212528

They knew about the events that transpired in Season 1. In 304, Deucalion tells Derek that he's "not a psychopath. That would make him like his uncle", referring to Peter.

My guess is that they came because Deucalion wanted a Hale in the Alpha Pack, and when news spread that there was a new Hale Alpha (in the same way news spread to Cora when Derek was building his pack and facing off against the Kanima, which got her caught up in the whole Alpha Pack mess), they decided to come to Beacon Hills. It just so happened that by the time they got there (at the end of Season 2, keeping in mind that the events of S1-2 transpired over the course of under 2 months), Derek was the Alpha.