How can I get the lover into the tower?

Hint 1 of 8:

Again, you'll need to get rid of the lancers and the chaperone first.

Hint 2 of 8:

And you'll also need to serenade the princess before she'll let you in.

Hint 3 of 8:

Move the lover to the square with a mandolin to do so.

Hint 4 of 8:

You need to find a mandolin that the lover can play.

Hint 5 of 8:

Go back to the book room and draw two princes for the princess on page 3. 
You can get a mandolin that way.

Hint 6 of 8:

Then take it to the lover, and have him walk to the tower.

Hint 7 of 8:

All he needs now is the key.

Hint 8 of 8:

And you should be able to shoot that down.