Can't be helped... they have lived with years worth of suspicion and mistrust. To have suddenly one guy say they have a safe haven. Yeah.. I'd have a hard time to believe it my self.
Isn't "Federation" the wrong term here? Doesn't it conflict with terms in later parts of the story by translating it as "federation"? In the novel it's translated as "Witch Cooperation Association".
I think its less mistrust and paranoia and more that bitch Cara wanted to be elder and have the power over the other witches. Such as the case of all worthless people who take leadership roles and can't take anything which threatens their authority.