Old Enough For The Truth

A group of four arrives back at their holiday rental after a fun day at an amusement park. Laura and Eric, the individuals who married Jordan and Oliver's biological parents, head off to prepare dinner, leaving the step-siblings alone. Jordan and Oliver enjoy the vacation but are cautious, wondering about their stepparents' intentions.
After dinner, Laura and Eric proceed to single out Jordan and Oliver in a suggestive manner. This prompts the step-siblings to inquire about the hidden agenda. The stepparents appear wary but confess the truth - they are, in fact, step-siblings themselves.
After they came of age, Laura and Eric engaged in a passionate relationship, despite their shared family connection. Learn of this forbidden love affair, they were estranged from the family and eventually went on to become a step-parent to each other's children Later, though they concealed their past, they couldn't deny their feelings and ended their previous relationships to be together. The revelation leaves Jordan and Oliver in disbelief and repulsion.
Open about their love, Laura and Eric propose a rather unconventional idea – a family orgy including all four of them.