how can you change your apple id on your phone

Create a new Apple ID and use it on one of the phones.

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 between the IDs 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.     

1. Tap the Settings icon.
2. Tap your name, which appears near the top of your screen (it should say Apple ID under your name).
3. Choose Name, Phone Numbers, Email.
4. Where it says Reachable At, click the blue Edit button.
5. A red minus sign appears next to your Apple ID. Tap the red minus.
6. A screen will pop up where you can choose Cancel or Continue. Choose Continue.
7. You'll get a screen where you can enter an email address. This email address will become your new Apple ID.
8. Look for a confirmation email at the new email address. You'll need to verify the email to complete the change in your Apple ID.

Note, if you change your Apple ID to an Apple email address (@icloud.com, @me.com, or @mac.com), you won't be able to change it back to a third-party email address in the future, according to Apple. The third-party email address you used before will appear on your Apple ID account as an additional email.

While you are editing your Apple ID, you can also add or remove phone numbers or email addresses from your account.