Potential summer trip with kids

You've slowed it down from what you were thinking before, and if this is something to shoot for, that's fine, but I'd suggest you approach it with an eye to easing it as you go. Throw in a couple of Jellystone/koa stops, maybe a theme park and make sure the oldest ends up dreaming of doing it again.
One other thought considering where you live and where your looking at going, be prepared for changes in plans due to elevation. Have the kids had any ear issues, have they experienced higher elevations? Some young ones struggle with it the first few times they are exposed to it.