Hmm, I don't remember if it was in a direct message, but I remember him saying that Patreon had clearly indicated to him that they did not want to have Myriam and Katherine having sex in the same room, and the scene where
Katherine sees Myriam with the cop while hiding, was done that way also because it is as far as he could go while being sure there could be no lightining striking him from Patreon, aside being of course a way to get Katherine more aware of some things (and some of Myriam's activities).
If you go back a number of posts, you should also see I was one of those who suggested to go the "triangulation" way to get around Patreon, including involving William and/or Katherine's girflriend, so I am certainly not against it.
It is very simple, in the basic and broadest acception, without getting into legalities, incest is sexual contact between two persons linked by blood (notice I wrote without getting in legalities, I know some jurisdictions expand and/or extend this definition), so in theory indeed it would not be common (aside porn games and porn videos) for a mother and a daughter to have sex at the same time with the same guy without any contact between them, but it would not be incest.
Nobody is disagreeing with you about that.
The problem is not us, is Patreon, what they told Zorlun, and whether Zorlun decides he can risk their wrath. If it was the last update of the game, he could do it without problems, but we are far from it.