I ran the battle. The PCs were delayed by some minions outside, while the werewolves set about their grisly task. The PCs managed to get inside, and found themselves battling a fearsome foe, wielding a massive log. The battle was vicious, but it all turned when the barbarian struck him with a silver weapon... and activated his axe's power, which forced a shapechanger struck to revert to their natural form. The fearsome werewolf quite suddenly became Bander Brickside, one of the senior grooms in Lord Gallant's stables.
He, of course, couldn't wield a massive log. And so his "throw the log" escape plan was foiled. He and the other werewolf battled, then made their escapes; they were both nearly bloodied, but they had enough hit points to survive the opportunity attacks, and so over the cliff they went.
The fact that they were there to slay the bastard son really made things work. It added a piece to the puzzle, and gave the players a sense that the villains really weren't there for them in the first place. And, since they knew his identity, they rode to Gallant Keep and started a witch hunt... They just missed the werewolves, who made violent escapes shortly before the characters could identify them. So next session will begin with my players setting out on the trail of a trio of werewolves, some of whom they've met face to face.
So to everyone who commented here, thank you. Your advice made for one hell of a session!