Took a quick look through the code, the issue is the "something else" that happens has no impact on the direction of the story at all. There is no "something else" path, just an altered conversation squeezed inbetween before it goes back to as no choice were ever made.
Those alternate pathes you are bringing up all the time and refering to as "just broken" aren't in the game at all, and by how the steps are labeled, aren't meant to get implmented at all.
edit: did some google search based on that "stepsis_photo_1.jpg" from the image folder, turns out her name is
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and is an Instagram model with some selfies and workout videos, no nude or pornographic content.
For any content past clothed selfies the dev has to rely on just similar looking models for future scenes with the MC's sister.