As it's called "Sisterly Lust", I have assumed just one Sister. I am near the end of the first play through, so i'll try again and see if I can get a different Sister, or if it's always the same Sister.
Thanks for that, I am playing through a second time and finding that out. You should know that I never pay to download, as I have been burnt so many times, but for good games, I always go back pay for it and don't even download it. Maybe that's something you could put in your sales pitch. "If you like the game, please pay for it"! :)