Add one? You mean apart from the obvious muscular brother and yet to become muscular younger sister already present? xD
We're on the same page. Yeah, the idea would be what you do in all Visual Novels, especially Otome game ones. You say the right answers with your romance options and accumulate affection points. Each person has a "route" and if you choose the correct answers and end up with one of them you gradually are rewarded with 2-3 sex scenes often paced out evenly in their route. You can do this for Michael, Jonathan and Greg and some of the other men in the series. Or you can even add some of the women as potential romance options if you're ok with that as well. I was just asking that you include a blood related brother sister route because you pretty much never see that in any visual novels, especially with a muscular heroine (and muscular romance option).
So it´s true, great minds do think alike. Never played Otome games, but I kind of had it imagined like you described here. Although I wouldn´t set a focus on affection points, simply progress the storylines of the characters and decide acordingly at some point. But I´ll cross that bridge when I come to it.
As for the potencial options: I mean, Gina liking both girls and maybe even Greg is kind of hinted in the game already.