Hello Pierre,
I don’t see really why they would have to communicate between them.
I have integrated Lora in OpenMQTTGateway to cover use case that require long range, and to enable an integration with home automation controllers like OpenHAB, Jeedom or Home Assistant through MQTT. But I’m not sure to use Lora for a flat is relevant.
At first I was more seeing such solution for people with big gardens.