Lambic blend has bacteria. A pure culture of brett b only has yeast.
I recall seeing the article, but I've not had time to read anything yet. Surely the brett is added a secondary vessel or bottling. In that case, I'd just use one yeast pack and split that between the two carboys. It's strong stuff and resilient to punishment (under-pitch, high alcohol environment, etc)
For 100% brett pitches, I make a starter per usual practice. They can be sluggish to start sometimes, but that's not a problem in a pre-fermented beer.