The double has been a perennial theme in horror. It probably started with Poe (most things seemed to start with Poe) and of course is seen most spectacularly in Stevenson’s Dr Jekyll and Mr Hyde. The William Wilson segment of Spirits of the Dead, directed by Louis Malle and based on Poe’s story, is a notable cinematic treatment of the theme.
When it comes to horror movies weird sisters have been a major obsession, usually with the sisters being reverse images of each other - one good and bad. Brian de Palma’s Sisters and of course Hammer’s Twins of Evil being examples. Twins or sisters with some odd link appear in most of Jean Rollin’s movies. Jess Franco’s Doriana Grey is another example.
The doubles theme is at the heart of the very underrated 1972 The Other. Another movie with this theme is Goodbye Gemini.
Doubled sisters also crop up in several movies that are not quite horror but have some affinities with the genre, Bette Davis in A Stolen Life and Olivia de Havilland in The Dark Mirror being particularly noteworthy.