For Yellowstone and Grand Teton - they both have non-reservable campgrounds you could fit into. We've never made reservations for those parks. However, we park the previous night nearby so we can get there early morning - or before noon at least.
Tetons: Colter Bay campground has 300 non-reservable sites. There's a concessionier campground right next door called Colter Bay RV and for that you'd need reservations. That's the best place to stay if you need hookups. Also in the Tetons a little further south in the park and closer to the town of Jackson is Gros Ventre campground - also 300 sites and no reservations. This is our favorite.
Yellowstone: Here's a good site for all of your choices and reservable or not...
Yellowstone CampgroundsIf you want full hookups in Yellowstone Fishing Bridge is your answer:
Fishing Bridge CampgroundHere's another good site for Yellowstone and the various entrance roads:
Yellowstone RoadsFor Rocky Mtn. Nat'l Park - Glacier Basin Campground in the park is very nice as is Moraine campground. The beetles have damaged many areas of trees in the park so it will not look the same as when we volunteered there. There has been massive tree removals but perhaps it just opened up the area so that you see more of the mountains. Neither has hookups. Outside the park in Estes Park are quite a few campgrounds but haven't stayed there.
Have a great trip!