When activating from a evaluation EULA, EBS is activated the same as Windows Server.
To enter in the key all you need to do is;
Right Click Computer and select Properties
Next click Change Product Key
Enter your product key for the right server role and click Next
Follow the rest of the prompts to complete the key activation. Repeat for the other two servers.
Next you’ll want to add your CALs
Start the EBS console and select the Licenses tab
Click Install CAL Packs and run through the Wizard
Finally assign the CALs to the users and devices as required
Thanks Nick for this guidance!!!