Bruh, guys from the start of this manga to the recent chapters, the relationship between the FL and ML (oldest foster brother), you should have already guest this to be about them. Anyway I get that they grew up together under the same house, brought up as brother and sister (not really in the beginning, but after the parents died), but they ain't blood related and their relationship is that of blooming admiration for one another (like very close friends), while it will soon blossom into a full on romance between the two.
So the incest tag is really not necessarily about blood related siblings it could just be about two characters brought up together under the intent to be siblings (not blood related of course), but amalgamated into a romance between sibling like relationships.
I hope you guys get what I mean when I say that.