Best cities to travel to in Spain from Seville...

You really need to look at the flow. I would start in Granada, then on to Gibraltar and finally end in Seville if those location are important to you. In someways, Gibraltar is really just a drive-by. Probably worth a half day at most. With five days I would consider skipping Gibraltar. Spend 2 nights in Granada and three in Seville.

I think you are planning too much. If I've understood it correctly your plan is go to Sevilla & sleep Sevilla; sleep Sevilla again; go to X & sleep X; day-trip to Y, return to X, sleep X; then go to Z, back to Sevilla, sleep Sevilla? Have you looked at the logistics, will you have a car?

But if you do this, then Marbella is probably the best base given it is between Gibraltar and Granada. Also, if not using a car I would expect there to be more, and quicker, coach tour options from Marbella to the other two. I'd also do Gib as Y and Granada as Z to make it easier to get back to Sevilla that night.

However, really I'd cut back. Marbella is the least interesting of the three places. Gib is fantastic with a lot to see in a small area, although it's not very Spanish (naturally, since its had the privilege of being British for so long). Granada is even better and has the Alhambra, which is unmissable, and much else. If it were me I would spend the two nights in Granada and just visit that city.

Steph,

Are we trying to see too much in that time frame?

Yes, I do think you have too many places for your timeframe.

Keep in mind that 5 nights translates to 4 full days to sightsee.
I’d suggest staying in Sevilla and taking a day trip to Córdoba; it’s an easy train ride.

You don’t say when your trip will be, but if you want to visit Granada, you really need to make sure that Alhambra tickets are still available for your dates.

If you’d consider spending the 10 nights in Spain, then you’ll have more time to explore some of the places on your list at a more relaxed pace.

Have a wonderful trip!

I'd put Cordoba ahead of the Marbella and Gibraltar -- The Mezquita was the most interesting thing we saw in Spain on our 2.5 week trip to mostly Andalusia and we saw the Alhambra (also a must IMHO although if you don't get to Granada the Alcazar in Seville is a close second).
https://janettravels.wordpress.com/2013/09/27/the-mezquita-at-least-the-catholics-had-the-good-sense-not-to-destroy-it-when-they-desecrated-it/
I'd also try to avoid bopping back and forth -- do whatever in say Granada and then head for Seville to finish rather than moving back and forth.

First, prioritize what you want to see in each location mentioned, what's a must and what you can do without. Day trips from Seville are going to be (2+ hrs. ea. way), so I recommend staying put there & enjoying everything it has to offer. Tickets & tours to attractions (Cathedral, Alcazar) give you priority not to stand in line, but restrict your flexibility. Recommend Marbella as #2 location. From here RofG is only an hour, and my personal favorite not on your list, Ronda (ancient Moorish city divided by a gorge) is only an hour. From either Seville or Marbella, Granada is 2+ hours, but the Alhambra should not be passed up (if you can obtain tickets for the day you want to go). It's like the Alcazar in Sevilla on a caffeine energy drink. We did a private 3-hr. tour & worth the money to get priority entrance & 800 yrs. of Spanish history. Easily a 1/2 day visit and then could leave for 2 1/2 drive back to Seville on scenic, excellent toll freeway to fly to Lisbon next day, or stay longer & check out the old city. If you can't do the Alhambra, substitute Cordova & the Mezquita.

I’d go a 6/4 split.

Day
1. Arrive Granada (2)
2. Alhambra
3. Train to Ronda (1)
4. Train to Seville (3)
5. Seville
6. Day to Córdoba for Mezquita
7. Fly to Lisbon (4)
8. Lisbon
9. Day to Sintra
10. Day to Belem & Cascais
11. Depart Lisbon