Blame It on Ginger(1986)

Two close friends -- Ginger (Ginger Lynn Allen) and Laurel (Barbara Dare) -- find themselves attracted to each other's fathers during a weekend getaway by the seaside. Before long, Ginger has bedded Laurel's dad, and Laurel has had her way with Ginger's, leading to all manner of complications, which eventually brings the two friends back together in a surprising way.