Re: multiple devices on one itunes account.
To add a little info to Laelipoo's post iMessage/Facetime uses email addresses as well as the device's phone number. You need to go into each device go to Settings, Messages. Go to Send&Receive and you will see the list of email addresses it is receiving messages (txt/iMessage). Uncheck on each device so that your wife's device doesn't have your email address and vice versa.
Adding a little info each person can have a different iCloud account but use the same Apple ID for the iTunes store which is what Laelipoo was saying.
Go to Settings, iCloud, tap Account and for your partner if they are logged into your iCloud log it out. This will not affect iTunes purchases. Then after it is logged out tap create iCloud account and follow the steps to setup an iCloud account for them. This will give them a seperate iCloud backup with 5GB but be aware it will also seperate Notes, Calendars, Safari, Photos and Reminders. So if you want to share any of that stuff you will need to share the Calendar, Photo Stream, Reminder list with their iCloud account.
After you finish just to check in Settings go to iTunes & App Store make sure all the devices are using the same Apple ID. It is independent of the iCloud.