ok, so I don’t know that platform, I use mosquitto with the configuration outlined here: http://www.steves-internet-guide.com/mosquitto-bridge-configuration/#:~:text=A%20MQTT%20bridge%20lets%20you,work%20as%20an%20MQTT%20bridge.
This may or may not meet your requirements but thought it may help… essentially it simply bridges the brokers via MQTT…
Otherwise, it could also work if you simply connect all your instances to the same broker?