It would be cool if they added those but they're probably skittish because Nutaku was censoring out incest scenes since forever.
I'm all in about Hero's mom n sis being added in harem.
Ya know, considering the Hero has never shown concern for people he left behind after he was recruited, he might be an orphan.
They may only bring in people from other worlds that won't be missed when they disappear. (Who here likes weirdly specific logic in their porn?)