Endgame (Grace and Carnby on the Ship)

Hint: How do I free Carnby from the witch's spell (as Grace)?

Hint: How do I (as Carnby) kill the giant ghost?

Hint: How can I kill the guards on the main deck?

Hint: How do I get the captain's sword?

Hint: How can I free Grace from her chains?

Hint: How do I kill One-Eyed Jack?