first up - not your responsibility at all - i would ask anyone who puked on my floor to leave also. you cannot control what happens to them afterwards.

secondly - i'm not sure if you can assume it was rape. certainly if your brother forced himself on her, or coerced her, or something, but you don't know if she wasn't the one who initiated it, or gave consent etc.

i think there are too many unknowns in this story for you to assume it was rape.

but if we assume she said no, or struggled, or whatever that made it clear she wasn't giving consent (or wasnt able to give it) - then yes it would be date rape by today's standards. it doesn't matter that they only met that night, it'd still be classified as date rape.

as for whether these things were common back then... i was born in '84, so i have no clue .