Unfortunately, I doubt the sister harem is viable, for the same reason Angela will never be a romantic option for Mike: they're blood relatives. I know, it's sad. Especially because it could have served to delve deeper into the protagonist's past, and how his breakup with Alexis affected those around the couple. Perhaps in the best-case scenario there could be a harem with Minami, Morgan, and one of the sisters (I don't know their last name, let's just say they're the Texas sisters), But unfortunately, never both sisters.Just two people blowing each other over the the skill issue that Andreal is pulling with the questionable Shawn story and other skill issue decisions and questionable artwork. Hell, I'm still waiting for Morgan and Alexis, hell even a tag team harem with Alexis and her yandere sis.
And lets be real. The Shawn game is a fucking pointless joke and honestly a waste of time and resources just for a spin-off.
Regarding the spin-off, I personally liked it, although I would have preferred sex scenes that were integrated into the story, rather than being something at the end of the route or only for the dates