First, the Guardian of Mana had waited until Scarlett had left his turf to start her apprenticeship with Fenagar.
The Fenrir taught newly appointed Guardians how to discover and master their bloodline abilities and then the Leviathan would teach them how to better use them for the magical research.
Salaark and Tyris were respectively the second last and final mentor in their initiation journey. Once a newborn Guardian had learned what their abilities were and how to use them, the Overlord would teach them how to tap into their full potential during the Forgemastering process.
As for Tyris, her role was to help them to reconnect with their old life and come to terms with their new condition. Many Guardians fell into despair because they felt they didn't belong among mortals anymore while others would believe themselves gods.