Actually, Xi Sai and Sean cannot truly be considered traitors.
Because they were never loyal to the Demon Clan of Chafne to begin with.
They were apostles cultivated over hundreds of years by Parren, belonging to the Old Demon Clan under the Primordial Demon. They were merely acting under Parren's orders, hiding among their own people in the Demon Realm, and even infiltrating the Enchanting Demon City to serve as spies.
Therefore, they are not traitors, but spies—
spies of the Old Demon Clan Faction under the Primordial Demon.
Using special magic tools provided by Parren, they managed to hide their identities and levels for hundreds of years.
Xi Sai even became a commander under the Enchanting Demons, which shows how deeply they were concealed.