I don't know the names of either of the fast biters. But I assume the not tied and muzzled one will not be to happy with his brother. Letting himself be tied up, as he may see his brother as doing, regardless of the fact he was rendered unconscious.
Agnog is the one who is tied up, Blackclaw is the one currently fleeing the valley, and Kragoth was the elderly father of the two who just died.
to be honest, Agnog was not particularly favored amongst his father or his brother Blackclaw. Agnog is your basic dumb sharptooth type, except maybe missing a few more brain cells. He's like the Sharptooth equivalent of Spike.
Though also to be fair, Blackclaw is not at all happy about the capture of his brother, as Agnog is all he has left for a family (aside from Blackclaw's closest cousin, Torgo, who will be apearing in the sequel RP)
hope that helps