Las apariencias engañan 1983

Screwball-comedy plot with most of the comedy scrubbed away: a millionaire is dying, and his niece and her boyfriend hire an actor to impersonate his long-lost son. The mechanics of the plot aren't really important, but the new household that the actor-guy assimilates into is full of different flavors of sexual non-comformity, all of which he gradually becomes comfortable with -- gay men, lesbians and a trans/intersexed woman whose state of being is what set the whole plot in motion.