You've lost me with your dates. I don't think you have as much time as you believe you do. If you arrive on December 26 and fly to Barcelona on Jan 1, you won't have 2 days in Cordoba, 2 days in Granada and 3 days in Seville. That adds up to 7 days and you will have less than 6, even before you allow for the travel time required to move from city to city. Perhaps you're counting a day in two different cities?
Dec. 26: Fly into Madrid and travel to Cordoba (2 nights?)
Dec 28: Train(?) to Granada (2 nights?)
Dec 30: Train(?) to Seville (2 nights?)
Jan 1: Fly to Barcelona (3 nights)
Jan 4: Train to Madrid (2 nights?)
Jan 6: Fly home.
All those 2-night stops will give you one full day and a few hours. In Cordoba you may be suffering from sleep-deprivation and jetlag on Dec 26, which would mean only one really usable day there.
If your main reason for including Granada is to see the Alhambra, you need to investigate ticket options immediately. The official website has no General tickets available in late December. There are a few Dobla de Oro tickets still being offered, but they could disappear at any time.
If there are other indoor sights you wish to visit, you should check their websites to be sure they will be open during your time in the city--though there are none I'm particularly worried about. You'll want to buy tickets for the Alcazar in Seville ahead of time to avoid an annoyingly long ticket line. Rick's guidebook explains how to avoid the ticket line at the Seville Cathedral. There are several sights in Barcelona for which advance tickets are even more critical. Let us know what you hope to see and we'll tell you what tickets should be bought ahead of time.
Five major destinations is an awful lot for a 10-night trip.