Spain in October

Option 1
Reduce travel time
Account for jet lag
5 - 5
I would add more days

I am 75 and our next trip to España is this October for 23 days.

Option 1.

I would not do Madrid, Barcelona and another city. Too much travel time. We recently did Madrid, Sevilla and Granada in roughly the same amount of time as you had. That was very manageable and a great trip.

You have nine full days on the ground; sleep-deprivation and jetlag are likely to dog you on your arrival day.

I wouldn't want to try to cover Barcelona, Madrid and Seville in that amount of time. Even Barcelona, Valencia and Madrid would be too much for me.

I'd stick with just two major destinations.

However, we've been warned that the area around Barcelona is suffering from a severe drought. It's conceivable that condition will persist into the fall, in which case there might be some impact on travelers.

I’d go to cities your mom want to visit, but would stick to only two with the time you have.

Madrid, Cordoba overnight or two, Seville could be a combination. Easy train route. Or, Madrid with day trips to Toledo and/or Segovia and/or El Escorial with a few days in Seville.

I agree with all who have said less is more. And, what does Mom think? (As also noted above)

She's leaving all the decisions up to me. She said whatever I decide she'll be happy with. A friend suggested I do Barcelona, Seville, and then maybe Lisbon...? Any thoughts on that?

No to Lisboa.
I love Lisboa and have spent 10 days there. Would like to spend another 10.

You only have 10 days. Don’t waste them traveling.

What do you and your mom enjoy? You've gotten good ideas - but without knowing your preferences - museums, cafe sitting, walking, exploring, shopping - impossible to provide much more.

Forget Lisbon. There is not enough time unless your style is "blow in, blow out" so I can say I've been somewhere.

ORDtraveler - I like museums, walking around the city, exploring, taking in the architecture. I love sitting at a cafe and just enjoying the time. Shopping is not a big priority for me, nor is partying and/or "a scene". My mother is a go with the flow type of person. She's just happy to be.

Option 1!
Slow down and indulge in the huge menu of opportunities available within each town.
What are your favorite hobbies? Seek to find like kind events/groups to explore for your hobbies in each location.

I try as hard as I can to not have a super long journey or a flight within a 10 day trip. Round trip Madrid would give you time for it and Sevilla and perhaps Cordoba, depending on your preference for moving hotels.
I would fly into Madrid, take train to Cordoba for a night or two, then Sevilla by train, then back to Madrid for the remainder.
You could also do Madrid and Barcelona, but that would be two large cities.

Another 70+ traveler here. Have been to Barcelona, the Basque country and parts in between and, recently, Andalusia. Have not been to Madrid. That said (as spectacular as Sagrada Familia is), my vote would be Madrid, Seville and Cordoba. The Mezquita is incredible, Cordoba is lovely and the food is great. Alternately, if you can fly into Malaga, then Malaga - Cordoba - Seville might be a relaxing itinerary. Enjoy!