Yes I would have thought that all the email accounts would have the 2FA activated however BT would appear to have created problems with this "update" and it may be that they have not all been activated.
If you log on to your MyBT which also has 2FA activated in the update, then go to "Your Products" the "Email,manage" this should show all your email accounts and their status for the management of the accounts. If you have not "gifted them they should all show in the "Active Email Addresses" section.
If they are "gifted" they will show in the section "Email Addresses you have given etc".
If they are all still in the first section, assuming you are the BT Broadband account holder under which all the email addresses were created, it should be your mobile number that gets notified however I have just checked with some of the email accounts that I have created and only the main account one which I also use formy BTID gets the 2FA request.
If you go into your MyBT "Your Profile" it should have the phone number that you want the 2FA to be sent to in the "Contact Details" section. You should be able to change it there if it is not correct.
Having said all of the above, the whole BT 2FA is a complete mess and while I used to have a fairly good grasp of how it worked due to the recent update I am now in the same position as the BT Team who introduced the update... that is clueless about how it now works!
