The horror musical comedy film Hillbillys in a Haunted House bears some striking similarities to Scooby-Doo, and more specifically, Scooby-Doo Meets the Boo Brothers. The concept of "splitting up" is present, one character is named "Jeepers," Jeepers jumps into another character, Woody's arms whenever he is scared, and the general tone and plot of the movie is very similar to that of a Scooby-Doo episode.
There are also significant similarities to Scooby-Doo Meets the Boo Brothers in this film. This film features an old Civil War plantation as its setting, features multiple ghosts running around the house, three of which are an ape, a skeleton, and a Civil War general's ghost. The Civil War general ghost is implied to be a real ghost at the end of the film. Even more eerily, the name of the mansion is quite literally the Beauregard Mansion!
This film came out in 1967, before Boo Brothers or the Scooby-Doo franchise, so it is possible that some minor elements of this film may have inspired certain ideas for Boo Brothers or the Scooby-Doo franchise.