... Unfortunately, there is no walkthrough of the game that clearly states the critical choices for the game. For example, I was never able to get lesbian scenes between sisters or BDSM scene with mother and aunt, which are shown in the gallery.
Actually the WT/Cheat mod does exactly that, for instance it lets you know which choices change your Morality, or the Lust/Submission/Love of the sisters and things like the proper path to avoid the NTR scene during Isa's kidnapping and what to choose if you choose Ruby instead of Nat for help of which IMO choosing Ruby is the better option.
The stuff you are talking about is the Extra stuff that is not in the Main Game but in the Scene Gallery only.
Edit:
I should have clarified that it is no longer apart of the Main Game is using the WT/Cheat mod but some was shown as a Bonus if you used Lain's mod in the past. That game code was removed from the current game code overhaul.