Granada or Seville or Both.

Is this trip for this year, 2017? Have you looked at a map of Spain?

The Costa Brava is not a town. It is the name of the Spanish coast up near Barcelona. It is very far from Sevilla and Granada.

Marbella is a town west of Málaga on the Costa del Sol.

Where are you flying from to Málaga? Somewhere in Europe, right? What time do you arrive? Perhaps you could fly directly to Granada, saving some time on this very short trip. Assuming you arrive on 15 December and depart Barcelona on 28 December, I'm counting 13 nights on the ground.

Typically you need 2 nights somewhere to have the one day between to see things.

Do you plan to take the train from Granada to Sevilla, from Sevilla to Madrid and from Madrid to Barcelona? If so, Loco2 is an easy place to search for schedules and prices and to make reservations. I've been noodling around with it for a trip in the spring. Be sure to register and switch to € if needed. It's too soon to book, but you can use a different day closer to now to check schedules.

I think you may be surprised at how long it takes to transfer locations counting checking out, checking in, getting to and from the train stations and the train ride itself.

My favorite resource to check schedules and see the route is DB Bahn. You can see routes up to 9 December today using it, but you cannot book Spanish train travel on it at any time.

It will not be warm, so coast town or not, it's unlikely you will do any swimming. You can Google for weather averages for your destinations in December and find lots resources, but you may need to convert from Celsius to Fahrenheit.

It sounds like you may be new to European travel. If so, be sure to explore every nook and cranny of this RS website, but especially the sections on Money, Packing Light and Theft & Scams.

Q1 - the beaches will probably be deserted except for an occasional fisherman or local walking a dog. If you want variety, Andalucia has plenty. Stay longer in Sevilla and day trip by train to Cadiz (if the weather's good), on the Atlantic. There are beaches and an interesting town to wander - just minutes' walk from the train station. Skipping Sevilla is not a bad idea, it's a horrible one ! ☺☺

Sevilla has lots to see and do. Catch a performance at La Casa de Flamenco. Take a walking tour, visit the stunning Alcazar. Enjoy the Plaza de Espana in the waning light of late afternoon. Visit one or more of the old residences - the latest to open is the Palacio de las Duenas. See how the 1% lived. Check the Royal Equestrian School in Jerez for horse shows. You can take a day trip by train, tour a sherry bodega (Tio Pepe is the most fun), catch the horse show, then continue to Cadiz by train or to Arcos by bus. Sevilla has the best tapas in Spain. Day trip to Cordoba for the must-see Mezquita. Cordoba is worth a full day, the best medieval center in Andalucia and lots of shops with local products and well-made souvenirs at fair prices. Or you can leave Sevilla early, store your stuff at the bus station across the street from the train station, spend the day and then take a late train to Madrid.

Unless you want to spend hours and hours at the art museums in Madrid, only stay as many nights as you need for day trips. Then head for Barcelona. Check for closures on and around the 25th.

Q2 - dunno. haven't been to either. Don't wait too long to buy tickets to the Alhambra. They always sell out.

@Lo.

Yes. The trip is in 2017. So if we want add Marbella to the trip, we will start from Malaga to Marbella and then to Granada. And if we plan Costa Brava, we would add it after Barcelona and mostly stay one night in Lloret de Mar. We are coming from India and wanted to save time hence decided not to opt for round trip. Train looks more preferable when moving between the cities but what would you suggest?

@Chani.

Thanks for the valuable information. Yes, I too want to add Seville in the trip, even if it means just for one night. Will try to cut down days in Madrid and try to accommodate Seville instead.

Your schedule as described has a single night discrepancy - give it to Seville, to allow for Cordoba.

December
15. Fly in to Malaga. Transfer to Granada (3N)
18. To Seville (3N)
(day trip to Cordoba)
21. To Madrid (4N)
(day trips to El Escorial and Segovia)
25. To Barcelona (3N)
(day trip to Montserrat)
28. Depart from Barcelona

The beach areas are not advisable in December when they are virtual ghost towns.

I've been to Las Alpujarras and parts of the Sierra Nevada in mid summer, and would think Las Alpujarras a far better choice for you in December.

I am wondering when jet lag and post-wedding fatigue will hit - but maybe I am looking at it from an older person's perspective :-) It's a long distance to come, so I understand your desires to see as much as you can.
Also keep in mind where you will be on Sundays and Mondays. Things tend to close early on a Sunday if open at all and many sites are closed on Mondays. If your must see site in a city falls one of these days but is closed, that might determine the reason to go there (or not).
Also take into consideration that things will start to close noon on Dec 24 to Dec 27th. Services may continue to be reduced Dec 26th.
Renfe (Spain's train system) changes schedule in December and may not be available to review or purchase until November. It theoretically loads 62 days before any date, but sometimes they load up an entire month at once giving you almost 90 days' notice, but last year's schedule change was closer to 30 days ahead for some routes.
Sierra Nevada will have snow (most likely), so determine your reason to visit. If cold weather reduces your enthusiasm, then reduce Granada by one day. Otherwise, I might consider reducing Madrid by one day.
Edit: Bus and train from Granada to Seville take the same amount of time right now due to train rail construction, so you can consider bus for Malaga to Granada and Granada to Seville. Otherwise, train is your best option - including Madrid to Barcelona.

Yes, I'd lean towards just 2 nights in Granada, and 4 nights in Barcelona, esp considering your desired day to Montserrat.

Others have answered this pretty well. We are going in March and April, so I hope any potential rail snafus have been worked out by then.

Assuming all is okay, we are most likely to:

1. Take the train from the Madrid airport to Toledo.
2. Take the train from Toledo to Sevilla.
3. Take the train from Sevilla to Cádiz.
4. Take the train from Cádiz to Granada.
5. Take the bus from Granada to Alicante.
6. Take the train from Alicante to Madrid airport.

Some of those "trains" around Madrid may be commuter trains, since everything seems to go through the Madrid Atocha station. I hope most of the longer distance ones will be high speed, fast AVE trains.

I will do some final research using Loco2 and Renfe as it gets close enough to our trip to see what will actually be possible. I will also check ALSA for bus schedules to see if a bus might be better. You can do the same. It will take some learning of how to use those resources, but only you can determine what would be best for your trip.

For the train from the Madrid airport to Toledo.
CHANGE AT MADRID ATOCHA

For the train from Toledo to Sevilla.
CHANGE AT MADRID ATOCHA

For the train from Sevilla to Cádiz.
LOCAL DIRECT

For the train from Cádiz to Granada.
CHANGE AT DOS HERMANAS

For the train from Alicante to Madrid airport.
CHANGE AT MADRID ATOCHA

Thanks, David. I am aware of the changes and that [almost] all trains do go through Madrid Atocha. I hope the turtles are still there.