You have the south of France (and. Monaco).
The French Riviera has some great views. And you can walk the cliffs or the coast or both in the same day. The drive along the coast (avoiding the expressway) from. Monaco through Nice then Cannes and on to Sant Tropez is really nice with lots of places to stop. Ranging from museums to cliff top overlooks with hiking trails. Historical spots and such. We picked up some food for a picnic in one little town, stopped at an overlook with a pretty island just off the coast (I want to say the island had been a prison?) and a nice park. It had an old US WW2 landing craft in it. These are the little things you find just driving around,
Of course you can take the train but are more limited to stops in towns and cities but still a great view.
Not that far away is Avignon,. Around Avignon you have many things but the old Roman Ruins at Point Da Gard (the aqueduct) and the Coluseum at Nimes we’re spectacular.
The old Walled downtown of Avignon is nice and has a feel that is not too touristy. And the Popes palace is nice.
And of course the you have the chateau of the loire valley. Which are truly spectacular. We stayed in an remodeled Chateau for a reasonable price and had a big room and a huge bathroom built in an old timber framed space. Very nice and breakfast was amazing. Fresh squeezed Apple juice in the early fall. And you can visit a lot of different Chateau with a range of things. We did not get into Clos Luce, Leonardo de Vinci’s final home as my father was to tired. But it has a lot of interactive things aimed at younger folks. We really should have spent an extra day at least. Oh well.
And or course you have the Historical locations of WW1 and WW2.
I personally would suggest you (re)watch RS videos on France and then have everyone involved do a bit of homework. Give them a couple days to research what the want then tell them to come to the table with a list of say 10 places/things they want to see in order of importance, then see where the lists overlap or at least are in the same area and plan from that. You may be amazed what they come up with. And it makes everyone feel like they have a vested interest in the trip vs being dragged along.
I know my siblings when they were teens were a bit of a handful on long trips like to Europe (I of course was a perfect angel 😇)
Well I hope that give you some ideas.