Secrets of a French Maid(1980)

Original title: Die Nichten der Frau Oberst

Frau Oberst has 2 young nieces who are very open with their sexuality. She hopes to find adequate lovers for her nieces and along the way finds herself in some precarious sexual situations. After a series of sexual encounters between just about everyone at the estate, the Countess drops by for a party where the nieces announce their wedding intentions.