I'm not quite sure where you got stuck, so I'll start from the beginning.
In your case, it sounds like you want to enable DMC in distributed mode on your License Master. That means that from that box, you can see the status/info about the rest of you environment.
So to do that, yes, you have to add the other splunk servers as search peers from your license master, which it sounds like you did. But after that, you now have enable distributed mode for the DMC on your license master (as opposed to standalone mode). Once you do that, you should see your search heads as instances. Just ensure they're all there and have the right roles assigned to them and save your changes. Have you tried that already? is that where you don't see the search heads enabled?