Great start on the game. I had set them as Step Sisters an Step Mom but yeah there are some inaccuracies with the script then, the favorite sister part can be passed over due to the step sister\ sister meh close enough. The "aunt" part though doesn't fit then and they keep referring to the dad as "my dad" not "our dad" so I dunno. Also made the choice for him to be "adoptive father" so MC wasn't directly related to any LI's.
I really hope this gets regular updates though, very nice content and flow of story is pretty nice.