Flowers in the Attic 1987

After the death of her husband, a mother takes her kids off to live with their grandparents in a huge, decrepit old mansion. However, the kids are kept hidden in a room just below the attic, visited only by the grandmother, and their mother, who becomes less and less concerned about them and their failing health, and more concerned about herself and the inheritance she plans to win back from her dying father, to the point of murder...