This is discussion archived from a time before the current discussion method was installed.
From YKTTW Working Title: Flirty step-siblings
Peteman: What's differentiating this from Not Blood Siblings?
Hylarn: I think this is supposed to be a case where the step-sibling bit is emphasized, while Not Blood Siblings is mostly a way to do Brother–Sister Incest without actual incest. Still awfully close though.
movie007: What about in cases where the teens fall in love first, and then the parents fall in love (or are revealed to have fallen in love)?