sharing Apple ID

I started with one iPhone. Then an iPod was added. Then another iPod. And now 2 more iPhones. The phones are all under an A T & T family plan. When setting them up I used the same Apple ID so we would all be able to get the same apps. I'm not sure if this is correct. It is causing problems because any apps that are added to one device it automatically goes to all the other devices. And calendar events are popping up on other devices. Also whenever a device is plugged in to the computer to charge or update, they all say katie's phone which is the original device. How do I get iTunes to recognize each individual device? Any help would be appreciated.