Reinhart77's initial theory turned out to be quite the rabbit hole. As a foreword, I'll just say I'm willing to take back what I said about Lydie being a civilian.
What were the colors of the Crystals, where were they located, and what magic is associated with them?
These details may add some tasty nuance to your theory.
White Crystal
Found in: Jova
Effect: Reveals floating blocks in Berkeley Mansion
Blue Crystal
Found in: Aljiba
Effect: White + drains Yuba Lake to allow access to Rover Mansion
Red Crystal
Found in: Aldra
Effect: Blue + summons a tornado at Deborah Cliff
It's not really the magicks and locations that caught my attention though. It's the colors, especially of the latter two. But first, here are two things we're aware of:
- The Crystal Traders were other vampire hunters (Reinhart77 admits the Vampire Killer concept art might have been for unused villagers, but the Traders' sprites sure look like they're wearing armor just like the Vampire Killer, so they've gotta be one and the same)
- Simon finished his Quest™ with the Red Crystal while the two Traders have the Blue and White respectively
Fanon and speculation ahoy:
If we ignore the White Crystal for a bit, we're left with Red and Blue. Castlevania lore just so happens to have two closely connected items of those exact colors. And they show up just fifty years later.
https://castlevania.fandom.com/wiki/Bracelets_of_Brotherhood
And guess who gave those bracelets to Juste and Maxim?
https://castlevania.fandom.com/wiki/Lydie_Erlanger
My addendum to Reinhart77's theory: Simon and his two vampire hunting buddies held onto their respective crystals. All three had grandkids: Juste, Maxim, and Lydie, who would grow up together as childhood friends. Years later, Lydie turned Simon's and Grandpa Kischine's Red and Blue Crystals into mementos of their friendship. The Red became part of JB's Bracelet and the Blue became part of MK's Bracelet. Both allowed Juste to save Maxim and Lydie during HOD.
This brings up an interesting idea. Maxim went on a "training expedition" when he was really hunting for Dracula's relics. He just might have used the Blue Crystal power in his bracelet to drain a lake in search of those relics, like Simon did before him.
As for the White Crystal, who knows? Maybe Lydie made an EL Bracelet for herself. Or maybe it became part of something else entirely. Something that would help another hero save the day by letting him see through evil illusions.
https://castlevania.fandom.com/wiki/Holy_Glasses