What he is trying to tell you is that if you go up to the search box, at the top right of this thread and enter the word incest, you would probably have found your answer.
If you did search for that word, you would have stumbled across 1 or 2 posts that mention that the 3 cat girls you can encounter and pay to have sex with are ... sisters, one is pure female and the other is a futa.
Technically, the game does have incest, but it does NOT include the main character having carnal knowledge of a sibling or close relative. So, if you are hoping to bone your relatives in this game, you're probably out of luck.