Hello MH Badgers,
Thanks for the question, and what a great question it is.
There are four different accounts you can be signed into on an iOS device: iCloud, iMessage, FaceTime, and iTunes and App Stores. Theoretically, you could be signed into four separate accounts for each of these. For your situation, you might want to create separate iCloud accounts for each device/person, and continue to use the shared account for iTunes and App Stores.
For information, see these articles:
iTunes Store: Associating a device or computer to your Apple ID
http://support.apple.com/kb/HT4627
iOS 6 and OS X Mountain Lion: Link your phone number and Apple ID for use with FaceTime and iMessage
http://support.apple.com/kb/HT5538
Frequently asked questions about Apple ID
http://support.apple.com/kb/HT5622
Thanks,
Matt M.