This may push your Granada stay a little longer than planned, but I've read that Granada has a really amazing city-wide winter solstice celebration. I intended to see it year before last, but ended up in Malaga instead, but it might be worth looking into.
Cordoba is an easy day trip (one hour by train) from Seville, so you may prefer to just do it that way and spare yourself an extra day of hotel-shifting. But, since it's all so close and Seville, Cordoba, and Madrid are on the same rail line, any way you choose to do it is pretty straightforward.
I spent Christmas 2018 solo in Madrid. The previous year, I was in Malaga and Seville in the run up to Christmas. I think they're all pretty festive and fun, but certainly Madrid doesn't shut down QUITE as much on Christmas day as the other cities so. However, as you'll be with your family, it may not matter as much to have a lot of things open (depending on your Christmas meal plans). I'd decide to spend the holiday in whichever city sounds the most appealing across the board.
This seems to be an unpopular opinion, but I found Ronda kind of boring. Very beautiful and dramatic with the gorge, but all in all, kind of meh. Perhaps others on the board can comment on how likely it it to have much going on right at Christmas; between the holiday and the season, I have to wonder how lively it would be.
I was similarly underwhelmed by Arcos. It's not that I didn't like it, but I just really didn't see the massive appeal. Of course, everybody is different, but I think if you consult others on this forum, you may find some other good, smaller city/big town suggestions. I also was unimpressed by the restaurants in Arcos (and while I like good food, I'm not a restaurant snob. I'm totally happy with a hole-in-the-wall place with great food). There wasn't much variety, partly, I am sure, due to the lingering economic hard times of the city. Of course, I was there in 2016, so many things have changed, but I'd do some more homework. How are you planning on getting from Andalusia to Madrid? If you're renting a car, especially, you'll have lots of options for less well-known gem-like towns where you can recharge before hitting the cities.
One last thing. I love Madrid and think it doesn't get as much love as it deserves, and, as I said above, I spent Christmas 2018 there. But, unless you're adamant about going (which is understandable, especially for art lovers, you might skip it and just make this trip about the south and a slow meander to Barcelona. You'll be cramming a lot into those days in Seville, Granada, etc., and may want a rest.
Caroline
