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: