My first choice is Davros, creator of the Daleks, and all out crazy-ass villain. He would always have his henchmen Daleks around as back-up, and would be a pretty nasty sight if you met him in a dark alleyway at night...
Second choice is Joffery, of Game Of Thrones and gory scenes fame. His entitled indifference and violent nature suit him perfectly to a villainous gang such as this. His flippancy and callousness are ideal for the pain and suffering of others.
Despite being from a film as innocent as Chitty Chitty Bang Bang, the Child Catcher and his sinister ways are enough to keep anyone up at night. Don't take the sweets, kids!
Finally, as the most despicable, sickly sweet character, and universally hated woman in fiction, Dolores Umbridge would easily be the final member, and leader, of this unlawful gang. Her pink manicured nails would tap on the metal of a screaming Dalek as she patiently waited for it to quieten down. Her whirlwind romance with the Child Catcher would be enough to put anyone off romance for life... and Joffery would be their adopted son, cruel and sadistic, but would run and hide behind Mumbridge at the slightest hint of real trouble.