!! Excellent questions!👀

On what I have for my lore, the people of Kalos would rather not talk about it. It is acknowledged but most would rather not discuss the topic. Much like ignoring the elephant in the room, so to speak.

Nellcher didn't heard of it until she accidentally eavesdropped Sinna and Dexio one time she visited the lab but didn't confront Augustine about it, she didn't want to make him relive those harsh times.

Eventually, Sycamore does tell her yet only one half of the story, the one every one knows. It isn't much later that he confesses about his relationship with Lysandre and how it affected him.

AND YES SHE DOES!! Nellcher has an Aggronite! And it's funny because Sycamore was the one that gave it to her 😆 he knew that it would turn Cinnamon even more strong (and scary) but he valued more the happiness of his darling ;; It was a surprise gift.