My immediate concern was more or less articulated above: it's well enough to plan a 3 year trip for yourself (with or without another consenting adult), but difficult to do so for kids. 10, 14, 16, or any other age: they're growing and changing so quickly that it's tough to predict how they'll be feeling about footloose world travel in a year or two. Plus much of what's developmentally quite appropriate--reorienting themselves to peer groups at the expense of family, for example--may not lend itself to what you're imagining.

Depending, of course, on lots of factors. I'm not talking about your kids specifically, or even your plans--merely stating generalities.

About your knee, again without knowledge of your specific situation... I've had several spine surgeries and a knee replacement recently (plus some other relevant issues, like surgeries on both wrists), and can report that what seemed crippling at first tends to require adjustments, not total changes within a year or two. For example, I'll never again kneel on my artificial knee, but I do ski (and fall), mountain bike (and fall), plus cautiously change out car wheels and do all sorts of other kneeling stuff. High quality, sports-based knee pads make all the difference.

I also drive long distances in my car, ride long distances on a variety of motorcycles, and even hike on mountain trails from time to time, paying in excessive stiffness and a lot of whining. You might no longer wish to travel with your own vehicle, but I'd suggest not giving it up just because you can't kneel easily and need to move around periodically. In fact, one of the benefits of having your own vehicle is that you can almost always stop (gasp!), park, and wander freely.

It's true that I've largely given up on long bus journeys and budget lodgings, and I don't sleep on the ground very often. However, these things were well under way long before my surgeries--when I was about your age, in fact. It'll be interesting to see how things line up for you.

Hope that's helpful, and as always if it's not please feel free to disregard any or all.

Mark