I think you're on the wrong track here. I started the game a few moments ago, but from your statement (that you live with the family of the "host") I think that it is incest. While you take the host's body... that doesn't mean that the blood relation is cancelled. So it's still incest even if the host isn't the original one.
I completely disagree with you. The MC is not a son or brother of the characters. The MC knows that they are not his sisters or mother. The body doesn't matter and has nothing to do with it.
MC doesn't even remember his family and he knows that the family he currently lives in belongs to someone else.
The body is just a container. This is not a game of incest.
Is MC related to the characters? If the answer is no then it is not incest, so the tag is wrong.
MC's real family thinks he's dead. It would be incest if MC were to resurrect and relate to his real family.
Probably the developer won't have a problem with the patreon with that story. All he has to say is that this is not the real MC family, but another. So he is not hindered by the Patreon.
For me it is not a game of incest because what really counts is the soul, the body of another is irrelevant.
But if you want to consider that it is, you who knows.