The Skeleton Key
Luke (Peter Saarsgard) and Violet (Gena Rowlands) are in on it together. They're really Papa Justify and Mama Cecile who put their souls into the bodies of the brother and sister and have been stealing bodies ever since (using Papa Justify's spell). Caroline (Kate Hudson) was hired to be the new body for Mama Cecile. Papa Justify and Mama Cecile win in the end and Caroline is wheeled away in an ambulance trapped in Violet's former body. Before the switch, "Violet" left the house to Caroline, so Justify & Cecile can continue to live there.
Thanks, Califia D!
(Links open in new window)
Read more about this film at The Internet Movie Database.