@Amairani Then why was Erich angry that Hari was treated as a Vastia in Chapter 34? "Oh, Hari, you're not a Vastia, you're an Ernst because you're my sister-in-law. Or better yet, maybe my wife. (???)" No, I don't think that was Erich's intention.
My point isn't that Hari was a long lost sibling, my point is the story is trying to make the idea that Hari has truly been accepted into the family DESPITE originally being a random girl. They aren't kinder to her because they better tolerate her, rather that they finally accept her as part of the family (or so I thought).
Yet Hari falling in love with Eugene contradicts that, at least with him alone. You don't fall in love with siblings regardless of age. And Hari came into the family when she was seven, mind you. If you can't be family because you get adopted at SEVEN, then I feel for every orphan who get accepted later in their life.