Two Honda 3000-watt gensets would not have to be "sync'd" to operate a fifth-wheel with a 50-amp plug, as each leg is completely isolated from the other, but you have to remember that you still will only have 25-amps per leg, not 50.
You'd likely be able to run both A/Cs, but adding in additional draws like microwave ovens, electric water heaters, and toasters might be a bit much.
Remember, at 120-volts, two Honda 3000s are 6000 watts, and a fifty-amp RV service is (50 + 50) x 120 = 12,000 watts.
Not exactly the same thing.
To answer the preceding question, yes, a custom "Y-Pigtail" would be the best way of connecting it all.