Right off the bat two question come to mind.
1. At one point do you stop the players who know each other?
2. What happens when the other players who don't "know" each other start talking since they see other players being allowed to do it?
I've had players tell me more than a few times, "Don't worry, Ref, we know each other." My response to them is, "As far as I'm concerned you all are strangers so stop." Look at it this way: what positive can come from opponents talking to each other during a game?"