My wife and I each use our separate iMacs, iPhones and iPads, with separate Apple IDs and iCloud accounts. No particular problems with those devices. We also have an older (late 2010) MacBook Air (running Sierra 10.12.6) that we share, with separate user logins. On the MacBook Air, I have no problem logging into my iCloud account with my Apple ID. My wife cannot log into her iCloud account on this MBA, however, even though she is logged into the MBA with her login. Am I doing something wrong? On the MBA I log out of my user account, then log in to her MBA user account. When I then go to System Preferences and try to log in to iCloud using my wife's Apple ID, this does not work. When changing over from me using the MBA to her, do I need to sign out of iCloud first, in addition to logging out from my MBA user account?