Yet another game where the literal motherfucking is lazily hidden with a find-and-replace "landlady"/"tenant". Dude, just commit to the incest or don't put it in at all.
As someone who does hate having dumb terms rather than the real ones in, this is not a valid complaint. This game offers you the options to set whatever terms you prefer for the "forbidden" relationships: you get a slide that contains three points, "name", "she is my X", and "I am her Y" whenever such characters are introduced. By clicking on the shown defaults you can overwrite them to whatever you want. This is done in-game, there's no need to code-dive or anything.
So, not only do you not understand why devs are pressured to adopt such concealing measures, you are criticizing a dev who went about such restrictions in the most easily revertible, player friendly way.