Did you remember to talk to the first blueskin before you killed him or just left him alone then came back up?
I havn't tested it yet but I am thinking that might be the problem because every time I have played butcher bay I would always kill him my first time though and never talked to him (the guys would never spawn if I did that), my theory was originally that you had to leave him alone and then come back up to get his friends to spawn and every time I did that I always talked to him.
I'll test it out later today to see if that is the problem.
Have you no shame? Get your dead ass up and fight me!