Phase rotation only comes into play with 3-phase systems (usually commercial/industrial) where each phase is 120 deg. from any other phase. Rotation is only a concern with 3-phase motors, inverters, and the like. The average home has 2 "hot" wires that are in-phase with each other. In this way, you get either 120V or 240V for larger loads.

Two generators get you double the wattage only by splitting up your loads across the 2 generators (and you'd need 2 transfer switches to do this). If one were to try running the output from each generator to one "hot" terminal in your load center, you'd have no idea what the phasing (and hence the voltage) was as the 2 generators would not be in sync.

Unless you've got electric heating, hot water, and maybe a well pump, I find it hard to believe you need that much power. And if you do have electric heat, water, etc. you might want to evaluate the cost of replacing or "upgrading" these components (especially if they're older and less efficient) because a 17KW generator is going to set you back big bucks and is only an expense, while more efficient appliances may save you money daily and possibly add to the resale value of your home (whether or not it cost effective is up to you and your circumstances). If you know an electrical contractor or a good electrician, I'd have him take a look at what you're trying to do.

I added up the power requirements for running my home in a minimal "emergency" mode (furnace fan, flourescent lighting refrigerator, freezer) and it was under 5kW even when allowing for motor starting requirements, but I've got natural gas heating and hot water.