There are many characters in Arnathia that are canon, including those in the Torgaro family (the Royal family of Orsholon) and the characters already presented in the Hargus Hurryhouse Adventures. Writing about these characters is perfectly acceptable, as long as those stories do not kill off or change any existing Arnathian history. Creating new events for these characters is perfectly fine, such as tales of a younger Hargus.
Characters that currently exist in the world:
Beivalur Feverbreaker Godthiraskime
Fazius Argenta / Fassnu
Rehonu / Reho
The entire Torgaro family.
NOTE: The Torgaro family currently has more than 145 generations created. Of these, less than a dozen or so have any lore attached to them, so they are ripe for stories. Also, only one side of each Royal couple has been defined in most cases, so there are ample opportunities for stories. Those who have already been created may also be ripe for new stories that help expand the lore of those characters.
More characters will be added here as needed.