Currently, there is no way for robots to directly communicate with each other, not even a condition based on other bots (like if another bot's hands are empty)
Maybe there could be a sort of indirect communication. A floor button would be built on the ground and the state of the button would be used as a condition for bots.
For example, imagine we have a robot that's needed to supply wood choppers with new axes. We could set it so that robots that chop wood will go to a button near the axe maker bot. The axe maker would constantly waiting until it sees that the button is pressed. When it is, it will build axes, and the wood choppers will then get off the button and retrieve the axe, and the axe maker will stop.
Additionally, you could make a button only accessible from one side and make the others walls, as to keep robots from pathing over it.