That's already been done. In the official release of the game, the MC is the son of a friend of the family. He's not related to any of them. You need to mod to the game to change that relationship.
That sucks. I state clearly in the SAZMOD that I have modded it's contents, but if it started in August 2016, that was 2 years before my mod came out. But I have even added a full on disclaimer now for the update I'm working on that says anything I add, which would include the choice to activate incest, is unauthorized and done without the developer's knowledge or permission. I guess it also depends on how stringent they are with the original code.
Saddog completely disable any incest content a long time ago. but there is still coding in the game for the old check to see if that's on. So they might be requiring him to remove all of that old disabled content completely to fulfill requirements. That can definitely take a lot of time as it's pretty much through out the whole code. It was probably just easier to completely disable to choice at the time, then remove it all.