Cindy And Donna (1970)

aka: Cindy & Donna

Cindy (Debbie Osborne), a 15-year old, maturing, young girl, and Donna (Nancy Ison), a 17-year old girl who knows her way around, are half-sisters. They live with their mother (Suzy Allen) and Cindy’s father (Max Manning) in an average suburban neighborhood. The girls experiment with booze, drugs and sex with multiple partners–including Donna with her stepfather.