We have several iPhones in the house all registered under the same name, how do I stop any changes made to one phone (eg downloading a new app, adding new contacts) being reflected in the other phones. I want each to operate independently.
I assume from your description that all of these phones are associated with the same Apple ID? If that is the case you have two alternatives:
Turn off the automatic update feature on each the phones and update each manually. Settings > iTunes & App Store > Automatic downloads: MUSIC, APPS, BOOKS, UPDATES
Get a separate Apple ID for each iPhone. Unfortunately that means you will have to pay for each installation instance for each of the iphones.