what if 2 phones have the same apple id

Create a new ID for one of you.

Apple ID - create a new.      

Apple ID – Create         

Family Sharing.         

Family Sharing - Set up.        

When changing to the new ID, there may be some data loss, but you can minimize it. If syncing photos with iCloud, ensure Optimization is turned off in Settings/Your Name/iCloud/Photos and/or in Photos/Preferences/iCloud. Then make sure full resolution photos are on the device/computer. When signing out of iCloud, if asked whether you want to retain data, choose yes. Messages conversations will be lost if they are addressed to the ID. See the article below for other places that the old ID should be removed. See Winston Churchill's response in the below discussion. Also set up Family Sharing to keep access to your apps/purchases. 

How to switch Apple IDs on your iPhone or iPad.      

How to transfer all files from one iCloud account to another.        

What to do after you change your Apple ID or password - Apple Support.     

Mskmn5508 Said:

"what if 2 phones have the same apple id wife's and my phone are using the same id. How do we separate them?"

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Apple Accounts Cannot be Merged:

Do you each already have your own Apple ID? If so, sign out of whomever's Apple ID, from whichever iPhone this applies to - then use the other Apple ID on the other iPhone.