Tyreese and his group are awfully trusting of new people, considering what they said they'd been through on the road. Interesting direction they're going in by having them side with Woodbury, though.
I hope the father and son get done in pretty quick, they're just plain dicks. First trying to get Tyreese to help them take over the prison, and then actively offering to help the Governor take down Rick's group. Hopefully the Gov will use them as cannon fodder.
Well, look at it from Tyreese's group's side. They just left a prison occupied by a group of pretty nice folks lead by a guy apparently bat-shit crazy, who drove them out. Then they run into the next best thing to civilization since the apocalypse. Seventy-some people in a walled town with most of the luxuries of the previous civilization - I'd side with Woodbury, too.
Woodbury is the best chance anyone has of establishing a real survivable community in the post-apocalyptic era. The only bad thing about it is that it's run by someone as psychotic as Rick, but who hides it much, much better.