Gotcha. I just read the setup, not the actual game (and post-mortem)...
Not sure what their rationale was for going 1/2 & 1/2 but it might be fun...probably makes it a little more difficult for the guards to pick the assassins, as each set of guards is only keying on one king. Only knowing one king, I can see the two factions of royal guards clashing more than they would if they knew both kings...could make for an interesting game.
I definitely would allow the assassins to talk, but you're right in not allowing the guards to speak...you really can't, as the whole premise of the game is that everyone is pretty much in the dark.