I mean, you can put always NTR out of the blue , cheating and stuff is common in real life. But let us analyse it systematically according to what we know about their personalities. I have not read all routes yet though, so I may be wrong. Please somebody correct me if that is the case.
There will be SPOILERS so read at your own will.
HUMANS
Mother, sister and ex girlfriend seem to be totally smitten by the MC almost from the beginning, with hardly any effort whatsoever (one of the reasons so far I don't care about them). I know there is some voyeur path with the Mother, but it looked to me one of your very first choices is given to the player to disable that
Lily is totally out of the picture too. She has her own problems related to getting close to people and my guess is that as MC helps her with that she clearly falls in love with him, if she is not already as there were some hints.
Jenn seems to not care about anything at all. While you could impose a NTR route with her, you would need to justify why that specific guy or situation triggers her interest. For now this may be the biggest candidate because we know very little about her.
INMORTALS
Mira and Caitlin have a potential very restricted pool of applicants, more like inmortal ones only. While NTR could happen with one of them, their personalities really don't seen to show any potential possibility. Mira is too uptight for that at all and Caitlin, while flirtatious enough that could suggest she may give an opening to other guys, it really does not look that way, as she seem more than interested in MC, at least in the route I read.
Sara seem to be the type of very hard to get woman. My guess is that her route will probably be one of the hardest to actually romance, as, let's face it, she is totally out of reach. Not only she is old and wise, she most likely see us as a child. It will really depend I guess on MC's powers and more. But honestly does not seem to be the kind of character to cheat or anything. Seems more like hardly anyone would be to her standards. But it could be my guess.
Honestly, I am totally biased when talking about the Baron girls, but I did try to be objective in what I know about them.
The way I see it, NTR seems very unlikely, so I would not worry that much for now.
I personally don't care and if Dev decided to include it as long as it make sense from a point of view of the story, I'm good. I mean, a situation in which you can fuck every girl with no consequences whatsoever and everybody is happy to share you sounds usually like bullshit to me, at least most of the time. I could understand it for a submissive character as the sister, but Sara would probably outright kill you. So if you act like a douche, I would expect at least some characters to react to that, maybe cheating on you, breaking up with you, killing, plotting revenge and stuff. After all, in real life, choices have consequences, right?
So as long as it is something that depends on MC choices, fine by me. I would dislike it if NTR is just forced for the sake of making an audience happy. After all you are a nice, attractive and interesting guy and you clearly care about your women. Forcing that they cheat out of the blue sounds totally against character as I explained above. So yes, if it is forced like that I would dislike it, the same way I would dislike a total fuckfest for the MC for the same reason.