I cannot stress how much it does not matter to me
how the game ends up justifying its incest. What matters to me is that the characters genuinely feel like they're family. To go through some of the games mentioned here that I have played, Now and Then is great, just as was said, despite it being adoption, you get the sense that this is a father daughter relationship, and that the father, especially, put a lot of effort into making sure that was the type of relationship they had.
For a Family Venture, I don't really feel it, tbh. It's a problem a lot of sandbox games have, where they rely too heavily on repeatable sex events, and not enough on fleshing the relationships out. I have enjoyed the game overall, but they no more feel like family to me than they do roommates. Also,
rb813 is correct, after figuring out you can definitely put them to sleep with the tea, you whisper into their ears as you touch them, giving them suggestions as to how their mind will interpret how the body is feeling in order to make them more susceptible to finding you sexually attractive. The biggest problem with the suggestion being, there's not enough tissue to make them feel like siblings or mom and son, so it's easy to feel like you're just a dude who's surrounded by gorgeous women who can't get any and is resorting to devious methods.
I played a bit of Guilty Pleasure a while back and decided I was gonna wait for more, but I did like how incest developed between the first two siblings, quite a lot, and how much the game focused on the familial relationship between the characters. I don't remember how many updates I've missed, but I should probably get back to that, because even if a slutty aunt dynamic enters to speed things up, I remember genuinely liking where things started enough, that it will be hard to fuck that up afterward.
On the subject of the tropes, ICSTOR has been around for a lot longer than they've been developing Milfy City, and they're one of the pioneers in the Daz 3d model AVN field, though their earlier titles are all done in RPGM. Between them, and their clone ICCreations (who are the devs of F.I.L.F.) a lot of the tropes we see in other games were shaped. Man of the House and Big Brother were competing when they came out to have the tropier story, and I think the only reason Man of the House came out on top is that Dark Silver gave up when Patreon started cracking down on incest. I'm sure a lot of these tropes were inspired by some japanese ones, but we definitely have a specific flavor with our online indy dev space.
Anyway... please, do not hold back because the game uses magic or sci-fi to make the sex happen. What matters to me is that the family feels like a family, and not just strangers who have names like mom or sis. Hell, blackmail, coersion, corruption, etc, can make it hotter, as long as the family feels like a family, and the result isn't that those elements kill that mood.