I think some parts would have been better if I was familiar with the Oriko Magica spinoff. At any rate I'm up to chapter 14 and it's moving much more smoothly. At this point I'm thinking that Ryouku is n pybar bs Znqbxn, juvyr ure tenaqcneragf ner cebonoyl Uvgbzv Fuvmhxv naq Xlōfhxr Xnzvwō (ylvat nobhg gurve ntrf).

edit: I appear to have mixed up maternal and paternal grandparents so I guess the second speculation above doesn't apply (at least not how I was thinking of it). Also chapter 14 clears things up a bit on this front anyway...