OK, just got off the phone to the 3rd Blizz representative.

Basically they completely messed up (his words!) and they need to downgrade and delete all 4 accounts, and I need to set this up again.

So basically I have my 1 main account again (Account A) and nothing else. And I'm going to do the following:

A > B > C

A > D > E

If I understand it correctly, this will allow me to boost the characters. Thanks for your help guys.