The Finians - The Fiosaiche, Druid Character Concept or Prestige Class?

In the Finians Tribal source book. First, I find this is a Druid character-concept and then I read it's a Prestige class, but I assume it's not, since the Fianna-Warrior is the only Prestige class fully set out and described.

Was this a mistake?
While on the subject of using the Finians...

Can I start off as a Humanoid (a word they use...) Witch/Thief with the Witch Character Concept Taibhsear, (Spectre-Haunted) and then later on multiclass even further into the Prestige class of Fianna-Warrior meaning that she is now a Witch/Thief/Warrior or does she need to start out as a pure Warrior to get that Prestige class?
Now, I probably know the answer to this going to be no, but will ask anyway...

Can a Warped-One have Witch as one of her class's (Talking about my Taibhsear/Fianna-Warrior here.) While it does say that the Earth-Power flowing through a Warped One cannot be easily coded into spells. They can still buy Sorcery. Just not as much of it as a regular human or El might?