This game is certainly unique. Your sister as wingman. Stats that apparently don't do much at all (haven't seen any mention of checks in the walkthrough). Going meta all the time (essentially telling to reload a save when you screw up the initial meeting with Ashley, Skylar going off about internet porn games, mentioning Patreon's crackdown on incest games etc. etc.). Being able bringing me to accept and even actively forcing something I'm not into - NTR, ditching the girls at the cinema to go out with Skylar to get the MMFF ending. And why should I deny Sis some pleasure if I'm not even in a relationship with her?
That said, even if there is apparently no sibling endgame I still would like to see some hookup. I mean she's teaching him all sorts of things, wants to cuddle up in the same bed, he fingered her, so there's not much left to escalate save for bjs, licking her and actually doing the deed. So unless interaction between them comes to a screeching halt there is not much wiggle room left.
Final thing: Thanks for keeping even the large breasted love interests in the believably proportioned category.