I think we ought to postpone this Haki debate for now.... after all, the full chapter's out.
So anyway, it should be noted that it's been confirmed that two days passed since the Sabaody incident. Also, the mark on the sisters' backs is actually the World Nobles' symbol, "The Hoof of the Soaring Dragon", which is meant to signify that slaves are less than human. Hancock also notes that not all of the Sun pirates may have been former slaves (I have a feeling that Arlong may have been a slave, though...).
What else....? Oh yes, it's been confirmed that the sisters were fed their Devil Fruits while they were still slaves for the sake of entertainment (so yes, Mero Mero is a DF power), and Nyon was the one who brought them back to Amazon Lily after Tiger rescued them, since she was still out of the country herself at the time. So, the sisters used their DF powers to deceive the rest of the Kuja and came up with that phony Gorgon tale to hide the truth from them (as we've already speculated).
Heh, one particular scene I found rather amusing is when Hancock called Luffy to her chambers. He was excited because he was expecting food, yet became disappointed when he found a topless Hancock waiting for him instead. You
know the reverse would apply if Sanji were in Luffy's shoes.
Still, now that Nyon's appeared, I hope we get to learn about
her past soon....