The Rats Are Coming! The Werewolves Are Here! (1972)

In early 20th-century England, the Mooneys are an eccentric clan live in a large rural home. Invalid patriarch Pa is a retired medical doctor claiming to be 199 years old. Phoebe, the eldest daughter, runs the household. Eldest son Mortimer is a businessman who conducts the finances and contributes to the income. Younger daughter Monica is a sadist who keeps live rats as pets, frequently mutilating them and other small animals. Youngest son Malcolm is a half-wit with animalistic tendencies to the point where he's kept locked in a room with live chickens. But the whole family have a dark, furry secret.