Connecting two instances - thermostat control

Hello.

I have a Pi 3 b+ running my main HA instance.

I would like to use a 2nd pi to connect to my Bluetooth radiator thermostats.

I have tried the MQTT Eventstream but the thermostats dissapear quickly and I can’t control them from the main instance.

Is there another solution.

I think it’s that the MQTT Eventstream isn’t able to control a thermostat entity and it’s real purpose is to just report sensor data.