Nine Guests for a Crime (1977)

Nine members of an extremely rich and hateful family have decided to have a reunion on a remote island in the Mediterranean. No sooner than their arrival, old grudges, resentments, and feuds make themselves known, along with allusions to some more macabre events in their past. But when their boats are sabotaged, thus stranding them without any connection to the mainland, it becomes clear that someone is not willing to let old wounds heal, a fact made all the more clear as bodies start to pile up...