After leaving Paris, we are planning to stay at a local hotel near Normandy, then another one near the Belgium border, then drive to the sites near each.
Frankly, that's just off the top of my head, and just one war. Their's Bastogne, of course, plus a whole lot more. I could spend half a year on the eastern frontier of Belgium just visiting the memorials for the Franco-Prussian War, around Metz and Sedan. Just tracing the movements of one French division over the first month of that war takes you to places where memorials for that war, WWI and WW2 are all cobbled together in the same half-mile.
And that overlapping goes back millennia... But, no doubt you already know that Belgium is a Battlefield.
Douaumont Ossuary and the Trench of Bayonets, both in Verdun. I can guarantee that images from both places will stay with you the rest of your life.
I see only one response among the ones here about the Romans. The Roman sites I visited when I was serving in Germany were quite well-done for documentation and I expect the ones in France would be the same. The recommendations you’ve received are all great on the more recent sites but I wouldn’t want you to overlook a Roman site by running out of time.
In Luxembourg, go pay your respects at Patton’s grave. For that part of Germany, Trier to see the Roman structures.
Get a tour of the Maginot line bunkers, they are hauntingly amazing.
Tour Anne Franks home in The Netherlands, not to far a drive. Remember this is what socialists want to do to us here.