Gotta say, a game like this could have a lot of potential. Some time ago I was looking for a game where you could just help the "rival" by corrupting or convincing the girls to fuck him. It is some kind of obscure NTR that we rarely see in games, usually Netorase is only about wives and the protagonist awakening a cuck fetish after some years of marriage, but in this, however, you help him to get the sister and probably in some updates, the mom (probably because I still haven't finished the game but at the moment it is mostly NTR with her, not so much NTS). I can't think of lots games with this kind of content, maybe A wife's phone can be an example with you corrupting the wife's sister or the stepsis, Imperium could be another example with that unfinished path about you corrupting the town for that black guy or the good son with you corrupting some girls that aren't exactly your girlfriends. And I give some examples so maybe I can explain better what kind of Netorase exactly I mean. So in that aspect I think this game is really interesting.
However, like some people in this forum already said, the lack of options is the main problem. Instead of... idk... the protagonist just submitting to Darren, maybe you could go against him and turn this into more of a netorare game (of course there could also be a "good path" but I think people playing this kind of games aren't here for that stuff). And of course you could also allow him to conquer the girls or even help like the cuck stuff that we have right now. I think having different options is what makes these kind of games a lot better. Mind plays a huge role in porn and maybe you allowing the NTR to happen or not could be a hotter idea than the protagonist just doing it for you, making you play a bigger role overall as the player behind the protagonist.
I wish the dev good luck with this game. This has a lot of potential and so far, in the month and a half that this has been public, I think it's doing good except for that main problem. Please don't abandon it like a lot of new HTML games with this kind of content that only receive some updates and then get forgotten (this could age poorly lol, I hope not).