[X] - Bullets and blades are to good a fate for them. Tie their hands and feet and let'em drop, one by one, slavers deserve nothing more than the cold depths of the sea. Let the captain be the last, let her watch what happens to man-catchers and flesh peddlers.
[X] Supposedly witches float in water. 'Check' that none of the crew are witches. Throw them overboard, if they float or resurface, shoot them for 'hypocrisy'.
[X] These people steal the sense of thought of children? Then steal their senses right back. Take their eyes and tongues and leave them on the life boats. Let them experience the clouding of senses they inflicted in their last moments.
[X] A form of decimation with their own hands (literally)! They were so eager to shackle children, executing adults should be no problem! Declare that they shall fight amongst themselves and the last alive shall be given freedom (by being tossed overboard to die in the storm)!
[X] Nail helmets onto their skulls like the children, stuff them in the cages (break bones to make them fit), give them no food or water and leave them to die in the hold.