Nest Thermostats can control up to 32 Zones if Nest is wired in through a 24-48VAC transformer. They should be wired together, and Nest's C wire should be connected to the same circuit as the other Nest devices.
If you are using Nest Thermostat with a Heat Pump or Gas Furnace, Nest Thermostat will only control Nest in Heat settings. Nest will not control Nest in Cooling, Auto, or Off modes.