Secrets of a French Maid (1980)

Julia and Florentine, two beautiful and perpetually excited sisters, reunite with their naughty widowed aunt, the sexually insatiable Lady Oberst, at her lavish, isolated estate. Of course, their reputation precedes them, and before long, men from all over town flock into the mansion of love in high hopes of having an unforgettable sexual adventure with one of the lady's nieces. However, Lady Oberst, too, is in dire need of hot, sweet love, and she's determined to fill her emotional void. But, what happens if Ninette, their seductive dark-haired French maid, wants a piece of the action, too?