There are quite a few issues you need to deal with -
- Are you planning to hire/rent one or more cars? Visiting many of these places really requires private auto transportation.
- Yellowstone can easily be quite wintry at high elevations by September/October. (I've been snowed on in Yellowstone in August.) Are you prepared for such conditions?
- Sixteen days, assuming that includes travel days, is a very short amount of time to visit all of these destinations. The Grand Canyon, for example, needs three days - one to get there from, say, Las Vegas, one to visit the park, and one to get back. The same thing goes for Yellowstone, except with Yellowstone you need more like four days to do the park justice.
- No offense intended, but why Kelowna? Do you have family there or some other compelling reason to go there? Not that there's anything wrong with the BC Okanagan, but it's not in the same scenery league as the Grand Canyon, Yellowstone, or even the likes of Whistler in BC.