Summer Dream (1990)

Grieved over the loss of their daughter, an elderly couple has decided do spend their vacation travelling around Europe. The cab driver who takes them to the airport, Leo, overhears their conversation and decides to profit from their situation: Leo convinces the couple's staff he's their nephew, and invites his friends and girlfriend over for a special summer. Things go awry when his friend Marcelo arrives with a bus full of teenagers, who believe the mansion is actually a summer camp.

Unfortunately the movie Summer Dream is not yet available on HBO Max.