Yes it would only be logical if they BOTH do it or BOTH have the choice to say no, anything else would not make sense.Again illogical. You mentioned the main character's sister. From your point of view, it would be more logical for her to fuck her husband too, since they're supposed to consummate the marriage. But that would ruin the game for a lot of people. Just like you're saying it ruined the game for you that the main character fucked his wife.
If no one fucked, mc and sister, it would ruin the game even more, as it would make even more branching that the developer couldn't handle. (not to mention dev's maybe planning pregnancy for mc`s wife pregnant in the story.)
So it's basically the most balanced solution, since I think you realize that just a small number of people are really worried about not being given a choice with Aurora or Isis.
Why on earth should there be any diffrense in that when they are both in an alliance marriage? both forced into the marriage.
Yes it would be one of the last thing i would want since im not into NTR but why ruin it for those that hate forced sex scenes? why does that make sense to you? while having a sister doing 100% the same but not being forced into the same as MC how on earth is that logical for you? the only reason your fine with that is due to knowing most people here hates NTR, maybe you do as well, so maybe just accept that some people hate forced sex scenes just as much as NTR and is allowed to complain about it, theres not even any reason to discuss the issue since its a forced LI and sex scenes nothing will change that fact, i just wanted to make my point clear how i feel about that kind of content and how it can ruin a game for some people just like NTR can and alot of other things can.
And your absolutly worng, if no one fucked mc and sister, there would be LESS branching not more, then game would be none sexual....also there is alot of people that hate forced LIs/sex/kinks/fetishes and so on and considering game was choice based for 4 chapters i dont think many would expect it to change to forced stuff.