France & Spain

If you are really interested in the D-Day sites, I want to discourage trying to see them on a day trip from Paris. It would be far better to spend at least one night in Bayeux. You could take a full-day tour the next day and still get back to Paris that night, though it will be rather late.

For me, Cordoba would be a higher priority than Cadiz or Jerez, but of course that depends on where your interests lie.

You should look at this question and response since it is basically the same regarding D-day beaches

https://community.ricksteves.com/travel-forum/france/mont-st-michael-and-d-day-beaches-in-one-day-from-paris

I would suggest shortening your stay in Seville and think about Granada. The Alhambra is a must see in Andalucia (book tickets well in advance) and the city has a lots of other sights as well. Also Cordoba is a nice day trip for Seville. I found fairly reasonable air fare from Granada to Madrid for a trip I'm planning in April...

Do you have 15 nights on the ground in europe ?

May
30. Arrive Paris (6)
31. Paris
June
1-4. Paris
5. Train to Bordeaux (1)
6. Train to Hendaye. Bus to San Sebastián (2)
7. San Sebastián
8. Bus to Bilbao (1)
9. Fly to Seville (5)
10. Seville
11. Day to Jerez
12. Seville
13. Day to Cadiz
14 Depart Seville

Thank you all for your speedy responses. This is our Fourth trip to Europe. Much to consider.

We've visited many towns and cities during our visits including Granada and Córdoba. This visit we planned to return to our favorite city, Sevilla, plus visit some new towns and cities-- the ones I listed.

We would appreciate apt rental (Paris) and hostal (area of San Sebastián) recommendations.
We rented an apt in Sevilla through airbnb, which we loved. However ended up paying a pretty hefty rental fee.

There are issues at the moment with Parisian apartment rentals. The city is in the process of enforcing new regulations, and it seems that many apartments are being taken off the rental market. Here's a recent thread on the subject.