Royal origins

While I'm still waiting for my first fanfic to be officially submitted, I plan on making another fanfic that will explain the early life of the Royal Sisters. It starts out with both Megan Williams and Twilight Sparkle being invited to join both Princesses Celestia and Luna for tea and other pastries. During this, Megan is still curious about alicorns with it still being on her mind ever since she came back to Equestria. Her curiosity leads her to ask the Royal Sisters to tell them their story on how they became alicorns, which I was always under the impressions that they weren't born such. Mentioning this tends to make Twilight herself want to know more about them due to her not even knowing this. I know some of you are going to bring up the book, The Journal of the Two Sisters, and claim that they were alicorns from the start, but I tend to find that hard to believe especially from an episode known as The Crystalling where they witness Flurry Heart being born and claim that they are normally not naturally born as this tends to be a rare event even for Equestria's history. Also, I know some of you will claim that because they predate Equestria, they could have been born that themselves, but if that was the case, they would have known that unless they got alzheimer's disease at one point and forgot about that. Also, the very journal that some of the bronies use never said anything about what they did before the founding of Equestria hence no mention about their early lives making that open to interpretation. More importantly, it was later claimed that the journal that talks about was long considered cannon to the show as the episode Horse Play revealed that they controlled the sun and moon at younger ages, which could give the possibility of earing those cutie marks even before becoming alicorns, which is what I find to be more logical, but you can always correct me if you think I'm wrong. For my story on this, I believe that they got their cutie marks first even though they found out that they were moving the sun and moon with their horns by accident without originally knowing about it, while becoming alicorns from a dream that they had in believing that they could unify each of the different groups of ponies. Although I do agree that they became alicorns at a young age, it's not said exactly how young, so that could have been when they were fillies, foals, or even just becoming adults. Again, input from anyone else is always welcomed just to make sure that I won't be putting anything contradicting the series itslelf.