I have connected any of the following in any configuration:
2 3500 Predator
1 2200 Predator
2 2200 Roybi
3 different regular inverters
They all get in sync when you connect them. Even when running under load. I could start both ACs in my 36 feet class A with a 3500 and a 2200 and then move the 2200 out for a few minutes, bring another one and connect it later, and the load would automatically balance between the two units, according to capacity. Don't ask me how, I don't know.
As a matter of fact, once for a Relay for Life event we had 3 RVs (1 A and 2 Cs) and 4 Inverter generators. We bridged them ALL and connected the RVs to them (Gen 1 - C - Gen 2 - A - Gen 3 - C - Gen 4). We were able to shut down one at a time, refuel, let it rest and restart and move to the next without a glitch.
Of course, we had to make our own parallel adapters, which took all but 30 minutes.