Want to buy new iPhone 15 pros while trading in old iPhone 7s + ACMI

1. Not entirely correct. Physical sims can be transferred to eSims from non esim supporting devices.
2. You should be able to use the AT&T App to get an eSim for your service plan and number that you can add to the new iPhones.

hyeminhan_2016 wrote:

In this complicated situation, if we are retail authorized users and I know the wireless passcode of the family plan, will Apple Store folks be able to transfer our current lines to the new phones (physical sims -> esims)? I made a phone call to the local store, but their answer was somehow murky, so I want to get your thoughts if you had same experience. Thanks!

You should be able to do so yourself from the AT&T app or website. The Apple Geniuses at the store, can help you with that process.

Get a new eSIM for your device ATT.com

https://www.att.com/support/article/wireless/KM1455633/

You need to have access to the ATT account.

Yes, the owner should be able to request the eSim for you through the website or App. If you have the account email and password for AT&T you can do it yourself.

1. That’s not a problem. Contact AT&T for assistance if needed.
2. That may create an issue regarding 1, above, if you are not authorized to make changes to the account.
3. You know what they say about assumptions… You need to verify that before you do anything else.
4. That’s between you and Apple.