Controlling Chromecasts on second HA via MQTT Statestream

Configuration
1

I have two Home Assistant instances (called HA-1 and HA-2 in this thread) running on two separate networks. They are connected to each other using MQTT Statestream and I now have the setup running so I get data from my MiFlora-sensor (connected via Bluetooth to HA-1) to the other Home Assistant instance (HA-2). This is done by including the specific sensor entity in the mqtt_statestream part of both HA-configs and by adding the sensor to the “sensor:”-part of both HA-configs. This indicates to me that I have everything mqtt-specific correctly set up.

My problem: I would like to see and control a Chromecast connected to HA-1 from my HA-2 instance. For now I have tried to add the entity (media_player.chromecast1) to the include part of mqtt_statestream in both configs, but without any luck. Is this even possible?
The Chromecast is for now added to HA-1 via the ‘integrations’-interface only. Should it be done manually in the configuration.yaml on both instances? Any other hints?

2

After many different takes on this: I have the same problem with mqtt_eventstream - even with two clean Hass.io installed RPI 3s. I can see the States on the Chromecasts/Google Homes from the Hass without integration to the units, but my service calls from the remote Pi don’t result in any actions on the non-remote Pi.