This thread isn't one of these sandboxes where you have to do the same stuff 10 times without success only to then suddenly advance one step in what's happening. If a dev does not want to include a certain kink, he won't, whatever the reason, whatever other devs do. Going on for months and months about the same stuff isn't going to help you, it just makes you look like a toddler who does not want to realize that there will be no chocolate before bedtime tonight.
I like the "Big I" as much as the next guy (provided they like it) but not every game needs to have it. Especially if it doesn't fit the storyline.
So to quote somebody else
Seriously. Accept that there will be no incest, decide whether this is still worth it for you, and move on into whatever direction. Just move on please.