Mouse clicking not working on Disk Utility screen. How do I select erase button?
If I understand your question correctly, you want to select a drive and erase it. However, while you've worked out how to select the drive using the keyboard, you're not able to select the Erase button.

In your situation you can do this with by using the ShiftCommandE keyboard shortcut.

Hope this helps. If I've misunderstood your question, please let me know.