Okay, now that I am in front of a computer, a bit more advice.

1. Between Atlanta and Savannah is Warner Robbins Air Force base. They have an excellent aviation museum there if you are interesting in that. https://museumofaviation.org/
2. Charleston - across the river is Patriot's Point with an aircraft carrier and the WWII destroyer USS Laffey. I think Folley's beach is worth the drive. Quaint little beach town and parks and lighthouse. In North Charleston there is the Hunley submarine from the Civil War.
3. Take walking tours of both Charleston and Savannah.
4. Do the Pirate House or the Pink House in Savannah. Yes, touristy, but historical as well.
5. In Atlanta, I would recommend a visit to the Ponce City Market, but you will need to drive. https://poncecitymarket.com/ . There is so much to see and do in Atlanta, but driving is almost always required. You could stay near a MARTA station, but not sure how helpful that would be. You can get to/from Buckhead, downtown, Decatur, but even then most areas require walking significant distances.

In Charleston, we stayed on Cannon St in an AirBnB complex. About a mile and a half walk to the furthest historical sites. But you are walking down interesting streets with lots of shops, restaurants, and places to refresh.
In Savannah, we also stayed at the River Street Inn, right on the river. Note, if you take the haunted Savannah tour and your spouse doesn't like ghosts, it does not help that one of the stops on the tour is the hotel you are staying at. Soooooo, we won't be staying there again.