To fit this adventure into Ptolus it needs to be flipped upside down.
As written, the party gets hired to locate a source of magic stone. Stories of heroes battling dangerous beasts give the PCs stuff to ask locals about in order to gain more information. The location is outdoors near some very small villages, cliffs, difficult trails, and a couple of castles.
I recommend putting this down in the caverns.
The wizard seeking the resource could be a member of the Inverted Pyramid, and more specifically the Dreaming Apothecary.
Change the Quoitine which is used to crafting earth based magic items, for Aethel crystals which are also prized for crafting magic items. The amount of Aethel available should be dramatically reduced since the value of the crystals is high.
Change the small villages into small dwarven outposts off of the Eternity Cave.
Take out Lady Penrhys' castle and replace it with the Abandoned Tower where an undead dwarf (wight) has taken up recent occupation. She's not aware that she's dead.
Swap Lord Gwebli out and instead have him be Lord Terrik Clanstone of Kaled Del. He'll help the party locate some important places if they do him the favor of taking down some Hell Hounds (instead of Worgs) loose in the caverns. Helping Kaled Del with the Hell Hound problem earns some good will from Lord Terrik Clanstone.
Keep the Galeb-Dur as-is.
Swap the huge ravens for Darkmantles. It will be a much more challenging and interesting fight.
You'll need to replace the random encounter table with suitable creatures.
The guardian of the Aethel is a Xorn obsessed with protecting the small supply. Consider giving it at least Lair Actions if not also Legendary abilities.
Since the Xorn cannot be returned to the Elemental Plane of Earth, which it wants, due to Praemel being a prison plane, another solution is needed.
Maybe Penrhys isn't the last of her family and that can lead to issues later on. If the family member returns, locates her body, and they use speak with dead they would only learn that the PCs killed her, not that she was undead when they did.
Think about having a rival adventuring company get alerted to the presence of the Aethel crystals and try to beat the party to them.