3Ph Inverter to 1Ph Interconnection

Merry Christmas
pvgreeze, Here are a few things to consider. The inverters are not identical and their outputs will likely not be synchronized with each other unless there is a connection between them to do that. Assuming that they can be synchronized the other issue is converting the three phase to single phase. To get full power out of the 480V transformer each single phase transformer would need to be on a different phase of the 480v system. Unfortunately this would make their outputs out of phase with each other so they could not be connected directly together in a single phase panel. You only have a couple of options really. One is to buy a phase converter which I don't think is a good option and the other is to do one single transformer (single phase 480V to 240v/120V). Unfortunately you will not be able to get full power out out of the inverters since you will only be using a single phase. The last thing that needs to be considered is whether or not you are synchronized with 240V/120V system that you are connecting to. Here again you will likely need some synchronization equipment (probably another inverter) to make that happen.
I'm addition to what ggunn said, multiple grid tie inverters will take care of the synchronization, you don't need to do anything or provide communication between them.