Scum of the Earth (1974)

Newlyweds Helen and Paul go to a backwoods cabin on vacation. When Paul goes back to the car for cigarettes, he's given no chance to ponder the carcinogenic ramifications as an ax blade makes the point moot. Panic-stricken, Helen runs into the woods, only to find Odis Pickett as her only savior. He takes her back to his place, where his pregnant wife Emmy, thick-as-a-brick son Bo, and available-since-she-was-12 daughter Sarah give her a real "family" welcome. Helen's immediate danger is delayed, but her newfound shelter shows signs of danger.