Reflections (1977)

The twisted passions of Uncontrolled Teenaged Lust...Reflect the fantasies of Youth! Bob and Connie and Joan are cousins. Connie loves doing to Bob what Joan refuses to do to Bob. Remembering her younger days when Connie and Bob would send her to her room, Joan chooses her welcome home party to pick and choose from her cousin's friends in defiance of Connie and Bob. Puts a whole new twist on Kissing Cousins! ERROR - Imdb is tt0127230 but number is taken by another movie at tmdb.