Haha, this chapter really cracked me up. The first page alone set the stage for the bizarre situations. Heck, even Luffy attaching himself with the legs into a centaur was too weird even for Robin.
As for the captors, my two guesses are that it is either a slave holding area or a classified WG facility. The captors have so far kidnapped a samurai's son and several child/baby giants. Either way, this is a hush-hush operation that even Smoker knows nothing about. The cell the strawhats in looks a bit too "modern" for mere slavers (marked as "Deck 102" on pg 7) so WG or other high-tech organization.
As to who is cutting people up and who the "Shichibukai" is and what he has to do with this is really anyone's guess. My guess is the person doing the cutting is Law or a new DF user. Most likely Law. My guess is that his crew was also captured. He either "cut up" the samurai before capture or after his escape.
The samurai hating pirates may have something to do with his being cut up by a pirate, or because pirates (or who he believes as pirates) kidnapped his son. Pirates kidnapping his son would support the slave trade theory, though the "pirates" are probably slavers.
The bird person is either DF or could be a member of new race of people in the new world–fitting into my theory of many exotic peoples and races of the One Piece world being captive on this island.