Apple allows you to set up multiple iDevices with a single Apple ID, but when you do that with phones and combine it with Apple’s iMessage service, you quickly get flooded with duplicates.
From the user’s end point, it makes a lot of sense to share an Apple ID, because it allows you to buy an app once and share it throughout your household.
The issue is that each time you add a new iDevice, it asks you to associate the phone number of that device to your Apple ID for use with iMessage, Apple’s combined Internet/SMS system. Most people are impatient, and most people will just click through merrily without thinking what that means.
What it means is that you’ll start getting iMessage chats sent to that person’s, and vice versa. Moreover, if you send them iMessages, you’ll get the iMessage back yourself. It quickly becomes a iMess.
Thankfully, it’s pretty easy to solve, and it doesn’t involve the kind of drastic action shown in the picture above.
Instead, what you should do is head into Settings>Messages, and there should be a section labelled “Send & Receive“.
Click in there, and it’ll list everything associated with your Apple ID. You can then simply choose which addresses/phone numbers you want associated with that particular phone, and untick the rest.
If you’re after sharing an Apple ID without sharing Facetime, that’s more complicated; you’ll need to register an actual email address with Apple for each Facetime device in order for that to work.
How Do I? covers the basics, because we’ve all got to start somewhere.