Hi! I'm the author of org-brain. I'm happy to see there's an interest for it. There's a screencast of me explaining it, which might give a better overview than the documentation: https://www.youtube.com/watch?v=3EGOwfWok5s
org-brain doesn't support more than one brain out of the box. In practice though you can have two folders (one for each brain) and change the path which org-brain uses, and thus activating one of your other brains.