When backing up their phones to a computer and then doing a restore, my friend's wife lost all her contacts which were replaced with his, and tiger calendars were merged. Any solutions to restoring her list of contacts and unmerging calendars?
Did she accidentally login to his iCloud account or are they sharing one? They can avoid these problems by using separate iCloud accounts. They can still share an account for iTunes and the App Store, and one of them can use that same login for iCloud, but the second one should have a separate iCloud account.
As Europa said, they will still need separate iCloud accounts to avoid this kind of mix up in the future. Also, having separate iCloud accounts allows each to have 5 gb of free storage. If they use the same account, they have to share 5 gb. They can share the iTunes Apple ID and share their purchases without paying for them twice.