The Unusual Suspects in this level you can get banzai earlier on in the game by placing your earth elementel 'stone wal' in the plant in the entrance near the reception desk hidden behind a wall (turn screen round if you cannot see it. Soon as he is placed there Banzai will be unlocked. Thats the only one i found so far.
WIERD SEANCE: Terror-eyes - Use Aether's Shattering song out on the veranda to break his glass bowl. Wendel - Scare one of the Jocks in front of him with spiders. (He says the look on his face was worth dying for!) There's another chained to the pinball machine, don't know how to release him yet. ;D
Those aren't "Hidden" ghosts. Those are the usual ones you can see in the panel and in the level. This particular thread deals with finding and freeing the ghosts you have NO idea exist in a level unless you happen to just stumble on how to free them (Like Bansai in the first police station level).