A battlenet account is something@somewhere.com
So two battlenet accounts cannot have the same email.

This is the same as two houses on the same street.
Even if they are next door neighbors, they have different addresses.

You would want the same name, address, billing information on the accounts.
And you'd be able to transfer toons from Account A on B.Net email A, to Account B on B.Net email B.

The restriction is, when a B.Net account (email address) is formed, you cannot transfer character to or from that B.Net account to a different B.Net account for 30 days.
After the 30 days, as long as all the other information is the same, you can transfer toons freely.