Well, thank you for that. I REALLY do not trust anything 'Fan made'.
If I recall correctly, the I-patch only adds like 2 dialogue lines,
where Grandpa outright states(to himself and Nina) that Kate and her daughters are MC's actual family. MC is not made aware of it, so story-wise it changes nothing. Just meant to make the player aware of the incest, but not the MC. As best I can tell, the incest is actually part of the game, just not revealed yet. Even without the patch, it's vaguely hinted at, several times.
Basically, you can use the I-patch, or not, as you prefer. It really changes nothing within the story, nor does it ruin anything. It's basically just an early reveal for the player.