From Glacier drive 191 to W. Yellowstone and on to Fishing Bridge. Towing your 26' RV through Yellowstone will be no problem. I'd advise to get to your campground and then begin touring.
If you could knock off 1 day for the Badlands and add it to Yellowstone that would be advisable. Badlands is basically a drive-through park unless you do extensive hiking in the high heat.
For the Tetons, we've always enjoyed Gros Ventre campground in the park.It doesn't accept reservations but there are 300 sites and rarely fills except on July 4 weekend. If you can get there by mid-afternoon you'll get a site. Nice open view sites with spaced trees and buffalo/moose roaming the campground. It's close to Jackson if you need a city fix or major grocery shopping. Definitely take the gentle float trip down the Snake River in the park. You just might see a moose in the water with you. We have! We love the Tetons and there are nice easy hikes to gorgeous places. Have a great trip!
