Good advice above from cruisingdad. You really need to figure out the AC amp load you might have in use at onne time. Wattage equals AMPS times Volts. So the KW generator you need is one that can supply MORE than 115 x whaterever your typical max AMP load is. A 30 AMP load = 3,450 watts or 3.45KW or about a 4KW generator. A 50 AMP load...generates 5.75 KW & needs a unit of about 7.5KW.
Can you live on the hook without both A/C's on? Can your battery charging be done while the A/C is off? What does adding the water heater into the mix do? Can you live without it? If so...you can save on size, weight and noise. Just check out your Ammeter while plugged in dockside under various scenarios and you can quickly figure what you need...but don't skimp or cut it too close as start-up loads can often be twice as high as running loads!