Sisters fight. Sister 1 slaps sister 2. Sister 2's boyfriend shows up out of nowhere and punches Sister 1 in the face. Sister 2 and boyfriend fuck. Sister 1 who is in hospital gets two horny studs and they, presumably, fuck like rabbits.
...You know, if the world actually worked this way, it'd be a happier place. As well as a more perverse one, but who cares about the details?