Sibling Rivalry/Brotherly Love

A list of films with one (or more) creepy, evil siblings, siblings in forbidden relationships, etc

Warning: List may contain possible spoilers.

Honorable Mentions:
The Brood
Village of the Damned
Children of the Corn
The Unborn (1991)
Suspiria (1977), Inferno (1980), and Mother of Tears (2007)

Suggestions are welcome.

Companion Lists:
Dads
Moms