Saw film multiple times in mid/late-1980s, possibly on showtime/Cinemax/HBO late night programming. Foreign film, possibly French.  Color. Stories starts with mother’s death, leaving behind two attractive sisters (one blonde, other brunette) with their stepfather. They immediately start seducing him (under his protest) as soon as they return from the funeral. They are successful on multiple occasions. Blonde had a blouse full of safety pins in which you could see her breasts. I believe they may have over-sexed him, as I think he also dies at the end.