This story is great. What I kinda don't like is that we know since chapter 1 they end up at the hotel. I would've prefer a slow build up to that. Also what happened to the big sister that she can flirt shamelessly with her little sister??
I think the biggest reason i'm such a fan of incest is the whole "strength of the bond" thing. Like, sure you can break up with your sister, but she's still your sister. There's something really precious about the idea that they're basically guaranteed to be in each other's lives until death.