well, technically this isn't really the way it should have been setup, and I imagine wasn't or else they would have been getting text messages, and everything else on ALL devices, including the wifes phone.

Each device associated with a phone, needs to have a seperate icloud id, in order for messaging, mail, facetime etc. to be seperate by devices. Of course, someone with a phone, puts the same icloud (apple ID) on the ipad and then all those same things - including calls if enabled - come to all devices. So, I doubt that say the wife had the same apple ID setup as the icloud login.

Now many people share the Itunes/appstore ID (also sometimes referred to as the appleID) and this allows them to share the same access to purchases, downloads, using the same CC for purchased on the appstore and itunes, etc. but this wouldn't enabled access to any and all messages etc, unless the user used the same email (must have been an icloud email) for both the icloud login AND the itunes/appstore credentials, and therefore one having those credentials could login to the account undetected - this is how the whole fapgate issue occurred. People used their personal email for the same login credentials, and someone could use a guessed at email address for icloud (and sadly often the same password) to login directly to icloud, and boom there were the picture backups.