December holiday break with 2 teens in Spain

I'd find that trip--especially the last half of it--exhausting and unsatisfying. It's unclear from your itinerary when you plan to move from one city to the next, but I don't like so many day trips when you have only 11 days in total. In particular, Malaga is a minimum of two hours each way from Seville, Ronda is a minimum of 2 hr. 15 min. each way, and Granada is a minimum of 2 hr. 40 min. each way. Those trips could be longer if you don't catch exactly the right trains to Malaga and Granada; buses take longer. Your only day trip from Seville that makes sense to me is Cordoba. The other places are just too far away, and including so many side trips is leaving you with only one day in Seville--a city that really deserves a minimum of three full days.

Rather than spending so much vacation time sitting on trains/buses, I'd drop Malaga and Ronda and spend at least two nights in Granada.

What's happening on December 26? What's your departure point for the flight to Barcelona? Will you be trying to see La Sagrada Familia through a sleep-depived, jetlagged haze? How much time will you have in Barcelona that day? You have only one other day in Barcelona. That seems way too little time to me. Barcelona has more points of interest than Valencia. Valencia's worth a visit, but including that city in your itinerary turns the 6-hour train trip from Barcelona to Seville into nearly 8 hours of riding the rails (spread across two travel days). I question whether Days 1 and 2 in Valencia will be more enjoyable than spending that time in Barcelona.

I urge you to go to renfe.com and check the train schedules for all the trips you're planning to take. Add up the travel time. Then add the time necessary to go back and forth between your lodgings and the train stations; that's likely to be close to 30 minutes in each direction, or one extra hour in each direction for each trip. How many days of your vacation will be spent just moving from one city to the another? Take the time to really enjoy the most important places on your itinerary rather than barely touching down in so many cities.

Spain is fabulous and teens and young adults especially like it. I always recommend Andalusia to people with that age travelers. That said, I think you have way too may long day trips. You could spend 4 days in Sevilla just seeing Sevilla. Granada is a long day trip, but the Alhambra should not be missed. You don't have long in Barcelona, but if you have interest in Girona, I'd certainly go. Girona was a highlight of our trip.

In my opinion, I'd skip Valencia and go to Granada for two nights and then head to Sevilla, possibly stopping at Ronda on the way (if you have a car). I'd spend remaining time in Sevilla. Cordoba is very special, I liked it enough for 3 nights, but very doable for a day trip, especially if you are organized. I wouldn't go to Malaga unless you are bored your last day in Sevilla which would surprise me.

We were in Barcelona for Epiphany and it was so much fun. Enjoy the parade.

EDITED TO ADD: I agree with acraven that La Sagrada Familia is less than ideal on a 1st day. But, it isn't a museum (well,there is actually a museum on the lowest level, but most would not consider it that appealing. Well, except for my physics minded daughter) My point is that La Sagrada is a 1-2 hour visit for most people and you could possibly "power" thru it. Again, not ideal.

The basic entry ticket to La Sagrada Familia (not including ascent of a tower) costs 26 euros for adults and 24 euros for folks under 30 at 2023 prices. To me that's a lot of money if you're fuzzy-brained. But again, I don't know that these folks will be. Maybe they're flying in from somewhere closer than North America, or maybe they can all sleep pretty well on an overnight flight.