Sorry, but there is no means to delete an iCloud account. You can cease using it, but they cannot be deleted.
Since the iCloud account and email are tied to the AppleID, you can change the password to the AppleID and shut down access to the email. But, that is also going to mess up app updates and everything else you've associated with that single AppleID.
No idea what to suggest, as it seems to me you've created a real pickle for yourself with that one AppleID shared by so many people.
P.S. If you change the AppleID password and tell everyone to get their own AppleID, you can still use find-my friends for tracking individuals with their devices - http://www.apple.com/icloud/features/find-my-friends.html although you would not have control of things like remote wiping and locking via control of the iCloud account on the device.