She’s not jealous. She’s only defending what is hers by right of birth. All those hussies are moving in, trying to stop the natural evolution of what Nature has mandated. :o
I’ve gone ahead and preordered the title for myself, simply on the merit of Sora. In any case it has meganekko, futago (serving double duty as imouto), meido, miko, oppai, and loli (or DFC at least)… so all the basics are covered.
I don’t think they’re twins: at least it doesn’t say they are. Probably “regular” sisters.