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This is directly from the comic wiki:
The three pigs grew discontent with being remanded to the Farm, so they conspired to stage a revolt. Colin's cousins sent him on a mission to Fabletown, working under the guise of a malcontent "pig in the city". His mission was to seek out others sympathetic to the animals' cause and recruit them. Having long ago made amends with the Big Bad Wolf (now known as Bigby Wolf), he took up residence inside of Bigby's studio apartment at the Woodlands.  Bigby didn't relish the idea of Colin leaving the Farm, but he was heavily involved with a murder investigation and couldn't be bothered to bring him back.
Now im not saying colin personally killed or kidnapped them but i think he is the mastermind