The hero has no blood ties. The mother in the game is a stepmother, and she has a daughter, she is a stepsister for the hero!
Blood ties or not, doesn't matter.
"Incest (/ˈɪnsɛst/ IN-sest) is human sexual activity between family members or close relatives. This typically includes sexual activity between people in consanguinity (blood relations), and sometimes those related by affinity (marriage or stepfamily), adoption, or lineage."
Or simply find a game that fits your personal interests. After all, devs see what the Patreon vote for. You suggested your opinion, devs take it in consideration. Join their channel and vote for what you'd like to see in the next update. Free content is for you to see, you want something that doesn't offend you pay to change it. There's plenty of free games. I'm also opposed to NTR, not my thing, but i don't pay to change it. Most I'll do is report issues. Not tell the devs what to do when i dont support their channel to continue the game. So take whats given to you for free and stfu. Dont like it? support for a change or Find something else.