I totally agree with you. The editable relationships were the best way the devs managed to come up with as a workaround that still allowed players to fill either the original roles or maybe something they were more comfortable with, even if some dialogues could become weird.
You'll only find those in content related to incest, so it's totally and completely possible to follow lots of works here on itch and still be your first time seeing it. The important part is that you're now aware of what it means when you come across it again, lol.
And it's possible that we may be from the same country, haha. Both the proverb and the legality of incest as long as consented and between adults fits the bill. xD