^ While you are correct that they're not technically aunt and niece, they are relatives. If I recall correctly, Zofia is from a branch family of the Nearls. However, Zofia and Maria are family, no matter how you slice it.
I've never really seen the appeal of omegaverse stuff. I skimmed over a few fanfics of that genre on ao3, and it's always seemed like just futanari where everyone is really mean to one another.