Lucia IS living with them. She is in MC house just for summer.
It's not about his plans. He fucked them. They know he can do it. Other females in game ( except Lucia) don't suspect anything from Hunter. At all.
Its all depends on dev of course. But from how i see them. They will just be in a way of the current story. For now we are playing this with mostly oblivious womans and battle between MC and Hunter.
And. Because they were fucked by Hunter. Not everyone here will like it. NTR too close for them.
Them returning would not remotely come even the slightest bit close to being NTR for anyone, how could it? They were in events long prior the MC even existing. As such its all past events and im sure its actually more appealing to re-build the broken bridge for a fractured family (they were victims after all) and beat Hunter at his own game with them bringing them into the harem under his very nose than just never addressing them in the story ever again especially with how angry the MC is with things right now. Sterling is understandably angry about a lot of things but he is unquestionably a good dude and it might even be the case he reveals what he has found to Lucia and she requests they be helped after what has happened to them instead of just leaving them victims forever more.
As for no one knowing what is going on, do they know either? As far i recall nowhere in the dialogue has Lucia said she has reached out to her family and made them awares that Hunter is back on the scene so they would likely be as shocked as he would be to return to find him on the scene as he was driven off at the same time as the rest of him but used the death of MCs father to worm his way back in. Sure they will know what he is capable of to much bigger degree but i doubt if they are looking to reconnect with the family they would come in and accuse the grandfather (who as you say the main girls are clueless about) of being a rapey perv drugging them with zero evidence as that would not go well with anyone they are trying to connect with again outside of Sterling who is in the know but is being blackmailed not to even back them up despite knowing this hence the premise of the story remains that NTR teased and often comically introduced but not actually NTR story.
There is plenty of reasons to bring them back, they would be far better received than Drew would thats for sure and many after seeing them stated outright they hoped to see them more in the story not just flashbacks. The fans would hate it is too vague a statement to make as a matter of fact, you indeed are not wrong that some would react this way but then i could hypothetically could argue far more would be pleased than unhappy and further thus most could be converted if the story with them is done right (as fuckable victims for MC to make Hunter miserable seducing but at same time this would make him even more Hunter in mindset than ever before which is what Hunter wants).
Still this is up to the dev but i feel we were introduced to them to such depth for a view to adding them into the story later as after all we didnt need BOTH to create the same reaction and tension with Sterling in the story vs Hunter or even regarding more sympathy for his dad and the way he reacted. In fact Lucia's mom alone would have been sufficient but we got the grandmother too which added nothing extra save was an extra nearest and dearest Sterlings dad found corrupted. Thats just my theory though, feels a lot of extra work with no payoff beyond an emotional sympathy for MCs father and of course more fuel for the fire to make you wanna fuck Hunter over time and time again as if that was ever an issue.
