Its a trope at this point, like there are way too many stories that start with something dark with the MC
It would be very weird to have incest scenes with the mother while the father is present. Or with the sister for that matter. But it also gives more room for the guy to become the "man of the house" and so on
On another note, the game is not as bad as you'd expect from it having half of its assets composed of AI - Including the images you earn from inputting the code. I think it has a cute and unique style. That said, I get one error per 2 actions that I make, and pretty much all the good scenes require no input from the user (imho the best scenes are the ones with the MC's cute blonde childhood friend). About AI, you can see why the guy is using it by the way the penis is horribly drawn. I also think this game has an impressively slow development pace considering he's using AI.
The existence of the grandma and that weird vomit scene are two colossal red flags though, so I suggest approaching this with caution
Honestly, it's probably not worth it, but considering there are so few interesting projects going on, I guess I'll bother playing it to see how it goes