This is beautiful
Tbh, I don't really know how far Patreon goes when tagging a game w/ incest (and naturally, I'm diving into this expecting to make some money)
But I agree w/ Corambis' take on it, 100%
Doing it the way Rey suggested would be the perfect and safest approach, but it does sound a little exhausting
And the story that I thought about kind suits it, I think (I'll explain)... and I hope the incest within ain't gonna be that obvious, on paper... obvious enough to trigger Patreon's police...
On paper, it kinda goes like this: your mom is not going to be your real mom, and her daughters are not going to be your sisters - she's your late father's widow, but she was never really a stepmom to you - you grew up living in the city, w/ your real mom (who's long gone), and to you, dad's new wife was nothing but your dad's new wife (who already had two kids when she married him, so you're not related)... that's it
But here's the trick, there's a lot more to it than that though that's the whole exposition you'll get... while playing, dialogues and all are going to uncover, real fast, how did your character grow up w/ these girls who lived under your father's roof, how did you relate one to each other while you were young, rarely seeing each other, but close nonetheless, and I want to quickly give the player the sensation that these girls and you, treat each like brother and sisters (each on her own way - one has your age and married, and the other is quite younger), and that you dad's widow do see you as the son that she always wanted but didn't get to raise, but this, this is her chance to finally get to you better, and relate to you
It seems a lot, I know, but I guarantee that you won't even need to ask me to have you calling them by mom or sisters - day 1 (the intro) is already scripted, and rest assured that the intro alone will have you feeling like these girls are family to you - initially, it'll exposition who they are and how you don't refer to each other as actual siblings, only to actually demonstrate a sweet but undeveloped fraternal relationship between you the moment you meet - that will develop as you go down their story, but not as traditionally as one might expect
And, as the game is NOT going to be build upon this - it's a harem sandbox, and every girl has her story (but the stories of the girls you live with will naturally unfold considering the life story you share, and the bond you never had the chance to build) - I hope I can avoid inflicting Patreon's rules w/ it