She's referencing the protagonists of The Beverly Hillbillies.
The Beverly Hillbillies is an American sitcom originally broadcast on CBS for nine seasons, from September 26, 1962, to March 23, 1971. The show had an ensemble cast which features Buddy Ebsen, Irene Ryan, Donna Douglas, and Max Baer Jr. as a poor backwoods family [The Clampetts] who move to Beverly Hills, California, after striking oil on their land.
She's basically using this reference to call their practices primitive. US 'hillbilly' stereotypes include banjo playing, inbreeding and crass, uncultured traditions and behavior (although these stereotypes are mostly broad and insulting). Dr. Albright is saying it in reference to Sally's casual suggestion of having sex with her brother Dick on his desk. Of course, they aren't really related, but Dr. Albright doesn't know this yet at this point in the series.
The Solomons, like the Clampetts, are plucked from their home and placed in an environment they're aliens to (only this time literally) and a lot of the humor is similarly derived from their own peculiar ways and their naive interpretations of local customs.