This is a relatively old documentary by the brilliant Louis Theroux.
It’s riveting. And frightening.
Update: The blonde twin girls in the documentary have changed for the better.

Although they haven’t completely unburdened themselves of their previous views.
Impressive as their transformation has been, for instance, their views on World War II still bear traces of the Holocaust denial ideology they were taught as children. For instance, asked whether the Holocaust happened, Lynx replied, “I think certain things happened. I think a lot of the stories got misconstrued. I mean, yeah, Hitler wasn’t the best, but Stalin wasn’t, Churchill wasn’t. I disagree with everybody at that time.”
Lamb concurred. “I just think everyone needs to frickin’ get over it,” she said. “That’s what I think.”