Well that's just silly. There's no reason to assume anybody in the game is related. There's literally not even a hint that some characters might be. It's basically forcing blood relations because "reasons". This was never even remotely intended to have any incest of any kind in it. (There's a reason there's no
incest tag on the thread.) Looks like the modder thought it turned out "great", but frankly I can't imagine how cringe-awful it's gotta be forcing that in the game.
I'm neutral on incest, so I don't care either way; but what is "great" is subjective, and I have my doubts.
Anyway.... The only way you'll know is to use it and see. I would make a backup copy of the original
script.rpy file and put that copy in a totally different spot, away from the game folder. Then,
in the
\game folder, drop that modder's replacement, and tell your device / machine to accept overwriting the existing file. If the mod doesn't work, you've still got the copy of the original so the game will still work; if the mod
does work, you obviously will know and can proceed without anything further needed.