I was mildly infuriated by the pseudo-incest so I tried making an incest-patch.
Sadly I'm neither a modder nor do I have any experience with Renpy to begin with, and even after 2 hours of trying to figure out how to overwrite translated dialogue I have no clue how to do so but I managed to change a few things about the mother, Dana and Chloe.
There aren't many dialogue lines during which their supposed step-relationship is mentioned anyway (only on the very first morning when they are introduced and maybe once or twice by someone else if I remember correctly).
So right now, their character descriptions call them "mother" and "little sister", Dana's and Chloe's age has been changed to "?" and I added two variables "age_chloe" and "age_dana" at the top of the .rpy so you can edit their age in notepad yourself.
I'm sharing it in case there's someone who wants to use it as well. Just place it into your /game directory.