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Hush can be unlocked by rescuing ALL the hostages in both the batcave levels and arkham asylum levels. You can see which levels still have hostages by the face next to the cursor when your selecting a stage. A frowning face means there are still hostages that need to be rescued.
Ra's can be unlocked by getting 100%. That means getting every minikit, red brick, buying every item in the store, and completing both the wayne manor and arkham asylum bonus levels.