Nahh, overriding the people who turned Sophia down isn't a dick move, it's hilarious. The people turning down Sophia and leaving her on the outside even though she's family are the ones making the dick move.
Unless
MoonBox has said otherwise, we have merely inferred that Sophia is the MC's half sister based on what Ophelia told us (which was very indirect). There's no guarantee that she knew for sure who the sperm donor was - I mean the mother is Annabelle, and I wouldn't consider her an unimpeachable source, by any means. That means that what Ophelia believes she knows about Sophia's parentage could be wrong. After all, if we're going to get all soap opera-ish, there's the possibility that a) Annabelle thinks she knows who the father is, but she's wrong; b) the baby was switched with another (deliberately or accidentally, with Annabelle's knowledge or without it).
On the flip side, we don't seem to meet a significant number of men who'd be old enough to be peers of the MC's dad in Gilford, any more than we meet many men in our age bracket. I mean, if this was intended to be a real dramatic mystery story, the status of the male population of Gilford would have to be addressed eventually; while I would find that an entertaining digression, I don't anticipate it actually happening. For all we know, almost everyone who was born within a few years of us was in fact fathered by the MC's dad, just like it seems the majority of people in Anne's age bracket will in reality be her half-siblings.
It's also possible Moon will never address this, so those who wish can believe everyone is actually much more closely related than is stated, and those who don't like that prospect can assume the relationships are just those explicitly stated. Being occasionally arrogant but still passive-aggressive, if Moon likes this, it will prove that he likes my theorizing; while, if he doesn't, it will mean that I'm too close to the truth and he doesn't want to confirm that. I find it always helps to plan out how you're right, regardless of what anyone else says (but I've been binge-watching South Park, so I may just be channeling a bit of Cartman).