OP here... Thanks for all the suggestions. Just a few answers to some of your suggestions. Generators are always stored without gas if not being used for longer than a month. So no fuel issues. I do believe the oil pressure switch is faulty on one generator. Will replace it.
I spent the morning load testing the generators. Connected each of them to a 1500 watt convection/toaster oven and let it run for way over an hour. Then put them in parallel and ran two convection/toaster ovens for over an hour. No issues what so ever. Then hooked them up to the TT and ran the air conditioner for two hours. No issues.
The only thing I can think of is I might not have had one of the connectors on the parallel cord fully seated.
