Triggering it is a bit convoluted but the way it's done ties in well with the game's overall theme of everyone's got secrets. The women the MC thought were his stepmom and -sister secretly being his biological relatives becomes just one more secret to complicate the picture. That said, it's mostly been confined to minor asides so far; perfectly possible to play the game without, if that's more your bag.
That's a problem with the text edited by his first proofreader. I'm (still) in the process of going back through the first 5 episodes (written before Royalcandy hired me to take over proofreading) and fixing all of the mistakes that are present in those five episodes.
Not a problem. I'm sure I speak for all concerned when saying thanks for doing this.
This actually should be less of an issue than it is. IRL most offspring that have been primarily raised by someone else then reunited with their biological parent(s) would have a hard time calling them Mom or Dad. But of course I understand your point of view, this isn't real life, it's a VN.
thank you, and specially trip with "mom" was awesome when goes visit 3am other room 
No. But I recommend you change your name.
It only fixes bugs in the achievements system of the original version 0.9.0 of the game and has no effect to any of the content, incest or not.
