I only read the first story by Kelley Armstrong.
Bobby is a child when he starts getting dreams of fantasy lands with castles and golden grass, the whole lot. He tells these to his grandmother, who then suspects him of being a changeling. A changeling is a faerie child left in place of the human baby when faeries kidnap it. This is what I don't understand. Your grandson has weird dreams and then you suspect him of not being human? Anyways, the grandmother starts to treat Bobby really poorly. Bobby's mother is actually a descendant of Cainsville, and Bobby finds solace in the only place who doesn't treat him like a freak.
We find more about Cainsville in this book. One, it's like a sanctuary for people who are different. The kids who have powers are treated kindly rather than shunned, the elders know rituals and spells and the ways of the old world, and it's basically a place where people can peacefully co-exist without suspicion and fear.
This book doesn't answer a whole lot of questions, but it does clarify some things. Cainsville is definitely not what it seems.