The Shuttered Room (1967)

On a remote island, the Whateley family resides in a decrepit mill, haunted by a sinister presence. Following the tragic death of her parents from lightning strikes, Susannah is relocated to New York by her aunt Agatha to escape a looming family curse. Years later, an adult Susannah convinces her husband Mike to vacation at the eerie mill. Their retreat quickly turns nightmarish as they confront hostility from a gang led by Ethan, her ruthless cousin, who seems determined to unleash the family's dark legacy upon them.