How can you connect multiple monitors to one temperature sensor?
You can have two readouts from one sensor by connecting the sensor to a transmitter. The transmitter does not need to have its own readout but it can send a 4 to 20 mA signal to two indicating meters connected in series.
You need to look carefully at the specifications to assure that the meters are designed to be connected in series. You also need to determine if the transmitter has a built-in power supply or it that much be purchased separately.
Here are examples of a 4-20 mA temperature transmitter and a loop-powered indicating meter.
Transmitter
Meter