But Alice from UTW (see my sig) is the MC's sister and the project is funded on Patreon.
I have understood with that game by doing a quick search, that in the Patreon all reference to incest doesn't exist, so from there, the danger of Patreon throwing the hammer is much less
Patreon obviously doesn't manually check every NSFW project for things that are banned (incest, rape, lolicon) because its
humanly impossible, but instead relies on algorithms that detect words, patterns, and user reports.
If the reports are enough, a member of the Patreon staff tests the product and if it finds the aforementioned incest, it is deleted.
In this case, the mere opening clarifies that the protagonist is looking for his sister, so it seems to me that the dev simply wanted to remove all the dangers from him by taking out the stepbrother's card.
As you say, there are gray areas and ways to circumvent Patreon's moderation like the example you gave, but I understand that there are devs who prefer not to take risks. What is a fact is that Patreon prohibits and chase those guidelines.
PD:
That being said, a simple mod would be perfect that remove the references that they are stepbrothers and return it to how it was surely originally intended (if that was the intention of the author, obvious)