By Kayla Kibbe When a new trio of young blonde bombshells replaced Girls Next Door stars Holly Madison, Bridget Marquardt and Kendra Wilkinson as Hugh Hefner’s set of live-in girlfriends for the sixth and final season of the show, it was easy for fans to write them off as a paltry substitute for the original stars that made the E! reality series famous. It was also easy to ignore some of the more troubling aspects of the new cast, like the fact that in addition to Crystal Harris, who replaced Madison as Hefner’s “number one girlfriend” and later became the Playboy founder’s third and final wif…