Well if you are talking about the captain, there should be a building NW of the Castle climb the stair case until you reach a Small room. The captain should be in there talk to him (and after a lot of arguing ) you will get the keys!
An NPC is a non-player character. Basically anyone who is isn't controlled by a player (Romeo in Varrock, Varrock guard).
Right in the center of Varrock.
just buy it on the GE......its called brass key
Varrock
A copy of the Varrock Herald can be purchased from Benny in Varrock Square for 50 coins.
You just said it, Varrock Library, Inside Varrock Castle.
yes he is, he's right by the varrock museum (which is north of the varrock east bank)
you get one from the guard in varrock castle at the top floor. you get the second one from the wizard in wizard tower in lumbridge. you get the last one from the drain and you need to go down to the sewers to get the key when it drops
Varrock church.
The Varrock Castle is east of the Varrock bank or northwest of the Varrock General store.
well go to the enstate agent in runescape
The Varrock Palace in RuneScape is located at the center of Varrock. It can be reached by running east of the Grand Exchange, running north of the Varrock Lodestone, and also by running south from the Wilderness. The Varrock Palace is most commonly used for quest purposes because King Roald is located in there.