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 not given a chance to ponder the carcinogenic ramifications as an ax blade makes the point moot. Panic-stricken, Helen runs into the woods, only to find Odie Pickett as her only savior. He takes her back to his place, where pregnant wife Emmy, thick-as-a-brick son Bo, and available-since-she-was-12 daughter Sarah give her a real "family" welcome. While Helen's immediate danger is somewhat delayed, her newfound shelter shows signs of danger.