Both email account A and B were set up under your dads BT Broadband account.
Unless he gifted BT account BT to you and you set up your own BTID the account would remain as one of your dads eleven email accounts allowed to be set up in his BT Broadband account.
When you moved away and got your own BT Broadband, you have used one of your dads email accounts, account B, to set this up and at that time set up a BTID in order to manage that broadband account.
Assuming you were not gifted email account B from your dad, when you got your own BT Broadband and used email account B to set up your own BTID with this email address you have in effect "hijacked" your dad's BT Broadband account to your BTID and MyBT and as such you are able to view all email addresses that were linked through your dad's MyBT.
What you and your dad should have done was for your dad to "gift" email account B to you and you should have set up a BTID to accept that email account.
When you got your own BT Broadband account you should then have imported email account B to your broadband account and this would have removed it from your dad's BT broadband account and left it completely under your control from your MyBT and it would have left his BT email account A completely under his control with no access to either email account except from the "owners" own MyBT or if they knew the correct password.
Hope that all makes sense out of a nonsensical BT email system!
See links.
How do I create and activate a new BT Email address? | BT Help
Can I move my BT email address to another account? | BT Help
Having said all that I think it will take moderator intervention to sort this out so I have notified the moderators of the forum about your problem. Once they have read this they may be able to help. They are very busy at present so it can take up to 48 hours for them to contact you. They will do this by posting on this thread.
