i'm sure you have caught on to this but just to be sure cause you seem to think there is suppose to be a distinction between roommate/landlady and sister/mother. but it's basically code in adult visual novels cause if they try and sell a game with incest things like itchi and patreon will remove their content. it's basically just the universal work around and if seen should just been assumed it's incest.
kinda in the same way an anime might have characters to go to "wacdonalds" for burger and fries. we all know what it really is but it makes it legal distinct enough to get around the drama that comes with it.
i get that's not everyone's cup tea but if you go into it not expecting that your setting your self up for unrealistic expectations.
i understand your not trying to tear this game down over it or anything and i actually haven't played this yet but i plan to soon. but it seems a bit odd that if something looks like a duck and quacks like a duck to be annoyed when it turned out to be a duck.