Southern Spain - confusion simplified itinerary

Have you plugged them into the appropriate search engines to check? (Renfe for train, bus requires some legwork.) Maybe someone will know...but it would help if you shared your airport. The flight home would be a big consideration for me.

D, but in reverse.

-4 cities in 10 days is a crammed itinerary, so I'd take the three-city itinerary
-There aren't great schedules out of Sevilla and back to the states on the same day. Presuming you fly out of JFK, I'd look for a two-leg trip JFK to Sevilla, make your way to Madrid, then a single, non-stop home.

Yes, your international flight options are key. It's great if you don't have to do that extra train trip back to the Madrid Airport, but for some of us a flight to or from Madrid (or Barcelona) is hundreds of dollars cheaper than departing from Granada, Seville or Malaga. The difference for me was about $500 (one way) in 2019.

If you find yourself in a similar situation, you can somewhat mitigate the time loss caused by a Madrid round-trip by heading right to one of your other destinations on your arrival day. Of the cities you mention, Cordoba is the easiest and cheapest to reach by train. By going on to Cordoba, you set yourself up for spending all your Madrid nights at the end of the trip and avoid the time-waster of checking in and out of Madrid hotels twice. Toledo works even better for this strategy, because it is much closer to Madrid and has fixed-fare rail service. That means you don't have to worry about escalating train ticket costs if you don't want to buy in advance because of uncertainty about when you'll actually arrive in Spain and be ready to get on a train.

Your trip is only 10 days, so you need to eliminate Granada (do it on another trip).

Do four nights in Madrid (taking in Toledo on a day trip), the two nights in Cordoba, then end with Sevilla for four nights.

Still, where will you fly out. Does Sevilla have a major airport?

I'm not good at fine-tuning itineraries that are already rather packed and finely-tuned, but you did ask for something logical, and I think you basically got it from Acraven, above. His suggestion of going directly from the Madrid airport to Toledo (I think that's what his suggestion was), then continuing through your proposed circuit, with Madrid at the end -- seems to be a good one. Just a couple of additional points:
I believe that a Madrid metro-area train called the Cercanias will take you from the airport to the Atocha train station, from where you can get the train to Toledo; but look into this.
As for looking into it: in addition to Spain's official "renfe" website (a Spanish acronym for "rail networks of Spain"), you may want to look into the Spain section of a website called "man in seat 61." The "man" covers passenger train systems world-wide, but does a remarkably clear, good job of it.

Acraven's thinking is logical, but it's contrary to my experience last fall. Then it cost a hair less for me to connect all the way to SVQ, and fly an open-jaw out of MAD. (Saving me not just those few dollars, but the train fare and significant time.)

I just looked at a random 10-day spread in September: JFK-MAD/SVQ-MAD-JFK was the cheapest. Then JFK-MAD round trip. Then JFK-MAD-SVQ/MAD-JFK. The difference in fare between the cheapest and more expensive... less than $100.

It depends on the origin airport.

Acraven - Of course. OP is on Long Island, so I assume my knowledge of pricing from JFK would be relevant.

Have you looked at flights yet? Sevilla's airport is small, you'll have to change planes in Europe, so probably Madrid. That seems to just complicate things. Malaga's airport is bigger, but there may not be any transatlantic flights, which means changing planes in Europe, so unless you get a really good deal on tickets going through some other European country, you're complicating things even more since you don't indicate a desire to spend any time in Malaga.

If you have non-stop flights to Madrid, that is usually better than connecting flights, eliminating the worries of missed connections and/or long layovers.

Then the only question is do you have enough time for Sevilla, Cordoba, and Granada. How many nights do you have in Spain? What time do you land and what time do you depart? If you land early in the day, you have plenty of time to get to Sevilla or Cordoba. If you fly out in the morning, you need to spend your last night in Madrid, you won't be able to get to the airport in time otherwise.

I’m going to simplify things
I’m flying from NY
I will have 10 days but only need to see Seville and Granada

So where to fly into and out of ?

Time is your most valuable commodity, especially while traveling.

For decades we have visited Spain and offer the following recommendation:

Using open jaw airfare fly to Granada via Madrid on the same day of travel preferably on Iberia. Most likely you will land in Madrid early to mid-morning and the connecting flight will provide 90 to 120 minutes of time to get from gate to gate. Suggest you use only carry on luggage to facilitate the connection. Using air travel to access Granada is most efficient manner to arrive without having to leave Madrid airport, commute to train station, pay and wait on train (we love the RENFE train system, but prefer the efficiency of traveling by air while already at the airport).

From Granada train to Seville.

From Seville train to Madrid.

Cordoba is great, and some folks would pick Cordoba over Granada, but with limited time we feel Granada and Cordoba overlap a bit.

Above recommendation provides same day connection to Granada.
Then one half day of travel to Seville.
Then one half day of travel to Madrid.
Thus minimizing travel stress and maximizing time on ground optimizing opportunity to create wonderful travel memories.

I like it!