Twins of Evil(1971).
Superb last film in the Hammer Karnstein trilogy starring Peter Cushing as Gustav Weil the puritanical witchfinder whose life gets complicated when his two orphaned nieces Frieda and Maria come to stay. Frieda is the outgoing one and falls under the spell of the depraved aristocrat Count Karnstein who is also a vampire.
Directed by John Hough this is an excellent combination of Hammer's old style films and the more erotic and bloody direction that the later films took.
Peter Cushing gives one of his most sadistic performances and is superb as the ruthless witchfinder. And the Collinson twins are excellent as well as the twins in their low cut dresses, in and out of them.
Highly recommended, and with a great rousing soundtrack too 8.5 out of 10.