Cascade control heat pumps

[Alain]

We have a Techneco Elga heat pump but have realised it's capacity is not sufficient. We still want to keep using it but are looking at buying another heat pump, a Sprsun CGK/C-22, and combining that with a boiler tank for domestic hot water.

We have a Plugwise Anna thermostat in the liiving room but Plugwise tells me they can only control one heat pump. I am looking for the possibility of controlling both heat pumps and, if needed, the gas fired boiler if it is really cold, in a cascade system.

Any idea's on how I could maybe do this through Domoticz? Maybe using MQTT and Node-Red? How would I control each unit? Through an Opentherrm Gateway? I want to be able to modulate the water temperature for maximum efficiency.