If it were me, I'd have made the Marc scenes patch-only rather than censor their relationship to no longer be incestuous, but it's not my game.
Well, for that "historical" element, I can help you understand why. One big reason was exactly because it was something done "a posteriori", after the incest was already in the game.
Making the incest patch would have meant having to redo pictures, game flow etc. already done, aside the fact Patreon used the scary technique of saying that if Zorlun was involved in releasing an incest patch *anywhere* (not only through Patreon), they would have kicked him out.
In this way, he could continue doing the images, and then someone else picked up creating an incest patch (and now someone else again has tried to create a partial combination between the incest patch and the WT mod).
I do not have the assets, nor the time, to do images and put them in a patch, nor the knowledge (could get it, but would add up even more to the time), and it is Zolrun's game, so, it would anyway be wrong, because it would mean I would actually be changing the storyline development.
In this way (images and story by him with Marc "not stepson", because Patreon prohibited even that, even without any blood relation, incest patch using the already present images by me), it allows the thing to work +/- decently for people who want to keep the incest line visible.
For the future father and brother situation, the thing may indeed be different, maybe Prometheus will pick that up, since he has the assets to create the images.