Sounds like you have logistics all figured out! That's awesome!
On the dumping - if you're between your double secret ultra private campgrounds that have duping facilities you can look for a Cabela's. I know our local one has a dump station for customers, and there's also an interstate rest stop near us that has one. You can find them on the Allstays Camp and RV app and I'm sure a big list is published elsewhere.
On the bunk beds for the grands - keep an eye on the size of them, kids can pretty quickly outgrow many of the undersized bunks that the industry puts in. They'll just be happy to be with you. When we camp with my parents we get ditched by our son in favor of my parents' fold out couch in their class A...Grandpa has Laurel and Hardy on DVD and will stay up all hours with him!