The notebooks as far as I can tell are magic. When you write in one, it shows up in everyone else's. Sort of like a magical phone call to everyone.

As for the castle, hm. The Lord of this place is nasty, if he learns a person's name he can take it from you and make you do what he wants you too. The guards were once people that he did that to, they lost their human forms and are bound to the armour. They're nice though, when he Lord isn't forcing them to be mean.