Help with how many nights in each city.

I could spend a week at the Prado Museum alone in Madrid... but not in one long visit.... saturation for me arrives in most places after 3 or 4 days...Of course you always miss things... But come back.... Toledo is a half hour train trip from Madrid and is a really great different experience. Each train trip except the Toledo one is half a day so build that into your activity scheduling.

Christmas could be challenging. Our European travels in a number of countries at vacation times (Christmas and Easter) tended to have us plant ourselves in one spot that offered a good larger hotel with food service since many things were closed. Check out the hotel offerings carefully. Another thought might be to spend Christmas Eve and Christmas Day at a Ski Area like Sierra Nevada near Granada which, of course, caters to travelers over holidays....even if you don't ski. That might require going to Sevilla first, then Granada for Christmas and then Madrid...

https://www.lovegranada.com/sierra-nevada/

Have fun!

FYI most restaurants will be closed on Christmas Eve (24) in Spain. Christmas Eve is a very familiar time for us, spent in one's house with the family. Even in big cities, it is almost impossible to find Spanish restaurants open on Christmas Eve. Try different cuisines, for example a Chinese restaurant or a Turkish restaurant. You will have a higher probability of finding those kinds of restaurants open on the 24th. Definitely reserve a table in advance for Christmas Eve and Day as well.

Also, be sure not to miss our Christmas markets in Spain! Our Christmas market tradition is a little know part of our culture (It's not just the Germans lol). Here is a English language article about some of our amazing Christmas Markets in Spain:
https://theculturetrip.com/europe/spain/articles/12-magical-christmas-markets-to-visit-in-spain/

I'd throw Cordoba in and see the Mezquita. If you don't want to stay over you could do it as a stopover from Granada to Seville. Would also take 1 night from Madrid or at least while in Madrid day trip to Toledo.

Thank you for your responses!
Good to know about Christmas season being low key… I’ll have to look into that more.
We are totally fine with just eating at Christmas markets 🤣if some of them are open on Christmas Day.
I will read through the article about Christmas markets.

Yes we plan to visit Córdoba and Toledo for sure as day trips!

Thank you!

I HIGHLY recommend Cordoba in this mix. The 3 great cities of Andalusia are Sevilla, Grandad and Cordoba. Cordoba's city is delightful. The Mezquita like nothing I'd ever seen, and there is more than just the Mezquita. We stayed 2 nights and could have stayed longer. I'd take the days out of Madrid, or one out of Madrid and one out of Granada. Madrid has world class art museums, but will the teens be interested in an extensive art experience? My kids all enjoyed art museums as teens but 3 hours was about all they could do.

It looks to me like a good plan. If you can make it to a Christmas service in Seville's massive Gothic cathedral I'm sure that would be a great experience. You might consider an overnight in Cordoba on your way from Granada to Seville, or Seville to Madrid, if you don't mind another hotel change. That would save backtracking as a day trip from Seville. The Mezquita at Cordoba is one of my "top ten" in Europe.

Toledo is great, best as a day trip from Madrid in your timeframe. It doesn't work as a stop on the way south to Granada or north from Seville/Cordoba because it has its own rail service from Madrid. I loved Madrid's great art museums but three teens might not want to spend as much time there as I would. It will be cold there in December, more so than your other places.

I'm sure the Sierra Nevada ski resorts are fine, but are you going to Spain to ski?

I like the itinerary and how you have it paced. One could always throw in extra cities, but I think adding another stop might be rushing things. From both Madrid and Sevilla you can always do a day trip if you wanted.

I join the others who suggest to add an overnight stop in Cordoba, taking a night either from Seville or Madrid (I would take it from Madrid, but then I am not a museum hound).