If I understand you correctly, there are two accounts and both of them are in your fathers name.
The terms of service allow for your father to have exclusive use of the accounts.
At his option, he can allow a minor child to have exclusive access instead of him.

He has basically gone with one account per child, yourself and your brother.
That means he is not allowed to access the accounts himself, the same as you're not supposed to use your brothers account or him to use yours.
There's basically no way for Blizzard to know if you, your brother, or your father is using an account from the same consistent IP address.
So technically you won't be caught if all the accounts are in your fathers name, but it is against the terms of service.

I'd imagine, you could have both accounts transfered from your fathers name to your name, if he was willing.
I'm not sure the procedure, but minor children with accounts in their parents names.. do eventually become adults themselves.
Even if you were to change your address, if you maintained exclusive access to both accounts, it would look like the family had moved.
Still, I'd recommend getting them in your name if possible; if you have issues down the road, it will be easier to resolve yourself then needing to contact a parent.