Flowers in the Attic | 1987
There are secrets Chris and Cathy never knew about their parents. After their father dies, the teenage siblings, along with their younger brother and sister, are sent to live with their cruel grandmother, Olivia. Olivia is disgusted by the children -- she knows their mother and father were actually cousins -- and locks the brood in the attic. The kids then try to keep their spirits high in spite of their bleak situation.