I’ve been looking into this, and I wonder if you can solve it by doing the following:
- Log in to your Account page: http://account.battle.net
- Go to the Games & Subscriptions section.
- Scroll down to Starter Editions & Public Test Regions.
- Click Create PTR Account and then confirm by clicking Create Account.
What I’m wondering is-- at that point when you log in, do you get a prompt for which one to use, allowing you to use the new one while Dad uses the original?