30-zone user here, and I feel your pain. While it sounds like a multi-controller dashboard is on the drawing board, it’s not here now.
If you need to keep them from running at the same time due to water supply capacity, you would simply choose which days each controller could run on a Flex schedule. In your case, I would roughly balance the load on the two controllers so each could water when conditions warrant. In the worst case, a zone gets watered a day later than it would like, which isn’t really a big deal at all.