Just saw this thread and can't help but appreciate the life experiences you'll surely have, good and bad, but experiences you'll relish the rest of your days.
The bikes you picked are obviously great choices, but I'm thinking it wouldn't be a bad idea to keep the three bikes within the same family of manufacturer, if not even the same model. By doing this, you'll be able to address problems AND get scheduled maintenance done on all three bikes throughout the course of your adventure, as opposed to jumping around a city to get work done on each bike. You'll probably be pinpointing dealers/repair centers along your route, so keeping that aspect simple will probably be a blessing. The bikes, except for the 250, are venerable bikes that haven't changed much in over 10 to 15 years, so you know those parts will be far more widely available in just about every locale you pass through, worldwide. When gearing these bikes up, don't neglect the fact that aftermarket seats will be a much appreciated expenditure!
While I've never made a road trip and haven't seen EU, Africa, nor Asia, I've been to many places in Latin/South America. As I'm sure you've experienced from your other travels, watch yourselves after you head south of the U.S. border. Besides all of the troubles going on predominantly in Northern Mexico, you'll find that the trip from Latin to South America is going to be questionable as to whether you'll lean towards a safe trip, or an adventurous one. There is a stretch known as the Darien Gap that seperates Panama and Columbia that is essentially unpassable to most motor vehicles but motorcycles. It's obvious you know people who have experience to lean on in planning this trip and you seem to be very thorough in your preparation, just err on the side of safety/caution to see this wonderful trip through from beginning to end.
Cheers, and here's to hoping you guys will blog your trip and allow the rest of us dreamers to live vicariously through your experiences. I wish you all good luck and good health!!!