Re: "iPhone XR: Apple Account won't verify: Each time we try to put the password in it says that it is incorrect.
We have changed the password many times but still won’t let us in."
Keeping an iPhone updated to the newest compatible iOS version can often side-step issues,.
You can check in Settings > General > Software Updates to see if there'a an update / upgrade waiting
(Please remember: it is always wise to back-up iPhone before updating iOS version)
You may just need to wait 24 hours for a new password to update everywhere it is in use (eg: FaceTime, Messages, iCloud etc.) Alternatively, you could try restarting the iPhone which may help update the recent changes / or restore order.
We don't know precisely where you are trying to sign in to the Apole Account: You could check you are correctly signed in (in Settings on the iPhone XR) to your Apple Account, with the correct ID and password.
See: Sign in to your Apple Account on the web or in your device settings - Apple Support
If you haven't already: Try signing in to the Apple Account online. https://account.apple.com/
If needed:
Get a verification code and sign in with two-factor authentication - Apple Support
If you have tried to access the account unsuccessfully too many times:
See what to do: If your Apple Account is locked, not active, or disabled - Apple Support