late April road trip starting from Paris

To make sure I understand, your plan is:

• Day 1: Paris - near Chambord
• Day 2: near Chambord - TBC?
• Day 3: TBC? - Dordogne
• Day 4: Dordogne - Montpellier
• Day 5: Montpellier - Nice
• Day 6: Nice
• Day 7: Nice - Paris

Am I correct?
It is a fast itinerary. Let me suggest a few tweaks first.

On day 1, you would have to leave Chartres by 13:00 to make it to Chambord by 15:00 and have 3 hours there before closing time at 18:00. Given that you need half a day to see Chartres, it makes for a very tight schedule. I would skip Chartres.

The Dordogne is out of the way; I would forget about Chenonceau and head straight to Dordogne the morning after Chambord, so that you have a full day there at least.

And regarding scenic driving from Montpellier to Nice, I would keep it to a minimum, because don't you want to spend a few hours in Montpellier at least? The most time-efficient scenic drive is D559/D6098 from Saint Raphaël to Mandelieu. For the rest you should stick to the A9/A54/A7/A8.

More broadly, I question the idea of a road trip from Paris to Montpellier then Nice with only 4 nights to play with. It's a lot of time on the road... You'd have more fun taking the fast train to Montpellier, renting a car there to explore the region for 2-3 days, then driving to Nice, or just leisurely driving from Montpellier to Nice with a few stops on the coast and inland.

Having driven every one of those routes, I can tell you that in reality they take much more time. For example, your 1.5 hours to Chartres from Paris is really 3-4 by the time you get to the rental agency, do the paperwork, inspect the car, get out of Paris, get lost, get on the right highways, get to Chartres, park and walk over to the Cathedral. It's the same for the other legs. And there's no time to eat, get gas, or use the restrooms.

You will see nothing except highways. I agree with balso that you should take the TGV train down to Montpellier, spend time there, pick up your car when you are ready to leave and drive to Nice stopping in a couple of places to see the sights. The south coast will more than fill 7 days.

I haven't been to the south coast (yet) but I agree with Balso and Bets that your driving + sightseeing plan is unrealistic. And what kind of vehicle will you need for five people and your luggage? Or will you have two cars, thus having to coordinate your driving and parking? You may have been using Via Michelin to plan your driving. Keep in mind that it assumes no stops, no traffic, no parking issues, etc.

Five train tickets to Montpellier next month might cost more than the car(s). If the economics of driving work better, then I suggest driving straight from Paris to Montpellier over two or three days. Bourges, about a third of the way along the fastest route, might be a good overnight stop. So might Beaune and/or Lyon, along a route almost as fast.

would you be overnight in Paris before leaving early to Chartres? Or are you flying in (maybe overseas) overnight and driving when you arrive (what time?)

Thank you balso, Bets, Dick and Nigel. Our itinerary is not firm and your input is duly noted. My nephew and friends made this trip in 2021 and had no issues. We will most likely alter things here and there as our reservations have some flexibility. Also we did not want to rely on train transportation due to recent events in the country. My daughter and her twin, who visited her 2 weeks ago, had many issues with canceled trains. We've reserved a minivan for our drive. Life is an Adventure

My nephew and friends made this trip in 2021 and had no issues.

Do not get us wrong: what you have in mind is feasible.
It is too early to be concerned about train strikes in late April, but anyway, 5 tickets will be expensive by now, and you have booked a car already, so if I were you I would indeed stick to your initial idea of a road trip.

I have a few additional thoughts:

• I stand by skipping Chartres. Assuming you would be at the car rental office of your choice when they open at 8.00 or 8.30, there is still no way you would get there before 10.30, leaving you with 2 hours in Chartres plus time for a sandwich.
• Chenonceau is out of your way, but after visiting Chambord you could stay in Cheverny and visit Cheverny the following morning if you want to see 2 chateaux.
• If you are set on Dordogne, try to stay 2 nights in the Dordogne; ideally somewhere between Sarlat, Beynac, Domme
• If you are not set on Dordogne, 1 night in Bourges was a good suggestion, and le Puy would be very good for the following night. You could then drive down the super-scenic N88 and D906 down towards Alès where you rejoin faster roads to Montpellier. A faster route, less carsickness-inducing, would have you stick to the A75 highway and stay in St Flour maybe (instead of Le Puy), not as spectacular but still a pretty town.
• If you stick with Dordogne, from there to Montpellier, you can either drive the more comfortable way via Toulouse and Narbonne, or on slower 2-lane roads via Rodez. Travel time is similar, but if it rains, go via Toulouse.
• For Montpellier to Nice, this map here is my suggested more scenic route. You see a bit of the Camargue flats at the beginning (+20 min vs. the toll highway), and you see the most scenic stretch of coast towards the end (+45 min).