Currently I have two accounts both of which are in my fathers name. One is mine, one was my brothers who no longer plays. Both are also payed by my father with his credit card.
For the sake of semantics (as we're talking about Blizzard's rules), lets first remove the idea that the accounts are yours but in your father's name.

The accounts "belong" to your father in as much as they belong to anyone but it's important to distinguish this in terms of Blizzards rules.

As a minor, you're allowed to play on his account no problem. So if he sets up more accounts on the same terms you're allowed to use those accounts as well.

Unless something drastic has changed, there's no implications for you multiboxing with those additional accounts. You are a minor using your father's account - the number of accounts, or how they're utilised, doesn't change that.