I would setup Family Sharing to allow sharing purchased media
http://www.apple.com/ios/ios8/family-sharing/
and have one setup a new ID using
Family Sharing and Apple IDs for kids - Apple Support
However, one person may have to start the game over using their own ID.
CHANGE ID
Apple ID: What to do after you change your Apple ID
The ID is used in the following locations and you have to change them.
Settings>Messages>Send and Receive
Settings>FaceTime
Settings>GameCenter
Settings>iCloud
and Settings>iTunes and App store
You have to sign out of ID (for iCloud you delete the iCloud account from the iPod) and sign in with other ID.
Note the following are resolved if you use Family Sharing (iOS 8 and later):
- Apps are locked to the account that purchased them.
- To update apps you have to sign into the account that purchased the apps. If you have apps that need updating purchased from more than one account you have to update them one at a time until the remaining apps were purchased from one account.
If the iPod has iOS 7 or later then you have the enter the password for Apple ID presently sign in Settings>iCloud.
Also, a Restriction can be set (Settings>General>Restrictions) the prevents changing accounts