This is our experience with being in Seville for Christmas about seven years ago---
All restaurants, bars, etc., begin closing down around 3, 4 pm. We had an early dinner around 4.30 in one of the restaurants but by 7pm our sense was nearly everything was closed. Earlier in the day we had a local guide on a walking tour. Her advice was shop earlier because little will be open on Christmas eve and day.
Earlier around noon - 1pm we had hit a local department store and laid in a substantial amount of non-refrig food for the next day or so -- cheeses, meats, bread, fruit, wine, etc. Our hotel had a small roof top garden that served us well for dinner. Our hotel provided a nice breakfast but no other food services. Our hotel did serve some hot wine and pastries on Christmas eve.
The only food services that we noticed in Seville that was open on Christmas day were the large hotel restaurants. And they were absolutely packed with long waiting lines. We made a couple of meals out of earlier purchases so we were fine with our roof top garden. There were a lot of people out strolling on Christmas day but did not see anything that was open.
I have no idea what travel will be like on Christmas day. I would assume services would be very limited and would wonder about taxis. Our experience with Europe over two Christmas/New Years travel is that Europe shuts down far more so than the US.
Things may have changed in seven years but I would plan for nothing to be open be prepared for picnic lunches and dinners.