The Guest (1999)

Giulia works for her father's law film and still lives in her parents' luxurious home. However, she soon realizes the young man from Thailand who is their new houseguest is not just a family friend -- he is Guilia's mother's lover, and almost half her age. Father, however, has an even bigger secret -- he's been having an affair with a man young enough to be his son.

Unfortunately the movie The Guest is not yet available on Paramount Plus.