Blackhand

Thanks @PsyCLown.
As you suggested, I tested settings propagation between the inverters and it was working fine. All up and running on the new inverters in parallel.
So I can confirm, the Luxpower portal really is only for monitoring, you don't need it to set up anything. You can't set up parallel monitoring on the Luxpower portal without an installer account, which seems a bit stupid given you can set up all the other monitoring. I primarily use Solar Assistant though, so not a big problem.

Try asking [email protected] to finish the parallel settings so you can use the luxpower app for monitoring. 

Hmm, I am actually not sure how necessary the parallel settings on the portal are to be honest.
I do it just because they say one should and it makes it easier to monitor, although I think it is just for that - monitoring. I could however be very wrong.
 
Maybe turn off the breakers which are meant to be fed by the inverters, then turn the EPS switches on and see what happens - without errors I doubt there will be problems.
I recommend 2x network cables, if one inverter goes down for whatever reason (maybe a firmware update) and you are only using 1x cable, then the inverter comms gives an error. I experienced this and it was no longer an issue when I added the 2nd comms cable.
 
Only indicator I am aware of is on the web portal. So that won't help in your situation. If the inverters are set to parallel and there are not comms issues, then the inverters should be taking to each other.
 
Another way to verify, I just thought of this while typing out this message, is to change the settings on one of the inverters and see if the setting change is automatically applied to the other inverter. If so, then you know 100% that the inverters are talking to each other.
Something like the AC First time settings should work well to test.