Train advice - seating and high speed routes

If you go to:
https://loco2.com/en-us
you will have a much easier time, at the same prices. It's where I bought my tickets at the suggestion of this great site:
https://www.seat61.com

Seville to Granada I highly recommend the Alsa Bus. I used that service two months ago It is quicker than the train
https://www.alsa.com/en/web/bus/coach/seville-Granada

From Granada to Barcelona, this route you should fly. The two cities are not all well connected by rail.

Or you can also use this site to book trains
https://www.thetrainline.com/?redirected=true

You can change languages on the Renfe site. Just click the white globe at the top right-hand corner and pick "Welcome". It will translate the page into English.

I've only rode turista class and the seats are fine. Much nicer than Amtrak or even the British trains.

The high-speed trains are much, much faster than the alternative. If you are seeing a mix of trains, it will be immediately obvious. The AVEs take roughly 2-1/2 hours for the Madrid-Seville run.

The AVE line to Granada isn't complete, so service in and out of that city is usually via a combination of AVE and bus. The two legs are coordinated, with the bus departing from just outside the train station. However, often sticking just with the ALSA bus is simpler and about as fast. The ALSA buses are generally comfortable.

Can't help with first-class tickets. Second class has always been perfectly fine for me.

As for seat selection, I think in some countries you take what you are assigned.

Edited to add: I'm afraid I don't know precisely what to tell you about a suitable time allowance for changing trains at Atocha Station, because I've never transferred there. However, the station is large, and I find it confusing. I think the train from Toledo may arrive in a different section of the station from the departure platform you'll need for Seville. You will probably need to ask a Renfe employee for assistance in getting to the right place without going all the way up to the main concourse (no disaster if you end up doing that, but you might still need to ask for assistance). I found the Renfe folks helpful, but you might not immediately see one, and you might have a communication problem with the first one you encounter.

There will be a very brief security check (luggage sent through an X-ray device) before you board the Seville train--unless that is somehow avoidable since you'll be transferring. There's also the issue of whether the Toledo train could possibly be late, which any given train might be. If not for the slight possibility of a delayed arrival from Toledo, I'd be comfortable saying that allowing a 1-hour gap would assure you a stress-free transfer. As it is, I'm gutless and am going to punt.

We traveled from Toledo to Sevilla last spring. My son is disabled, so we are slow to make connections as well. I allowed us one hour at Atocha between arriving from Toledo and catching our departure to Sevilla. It was plenty of time. I think 30 minutes would have been a little tight for our first time, but I would feel comfortable booking that now that I have been through the station and know where to go.

Edited to add: look for the elevator (acensor) in the track area that will take you up to the trains departing for Sevilla. Ask a Renfe employee if you can't find it. Taking the elevator will speed up your journey through Atocha.

When booking tickets via Renfe:
If you click on the "Welcome" button at the top of the Renfe home page, it will load in (mostly) English. Subsequent pages may be mixed English and Spanish. After you input your departure (Madrid -- Todas), destination (Sevilla -- Santa Justa), date, and number of passengers, you will then get a list of available trains. The AVE trains are high speed. If you click on the "Opciones" (options) plus sign, you will see a list of available classes (clases) and fares (tarifas). Preferente is first class, Turista is second class. Promo fares are nonrefundable and do not allow changes; flexible fares do.

Promo fare does not allow you to select your seat, but if you are traveling with multiple people, your seats will be automatically grouped together (assuming seats together are available). I think (but I could be misremembering), that you may get to see the assigned seats before you purchase, so that if you don't like them, you can cancel and start over.

I found Renfe easy to use, but I speak Spanish :-) If you have trouble with payment, use PayPal, which worked flawlessly for me.

This TripAdvisor link was helpful to me for using Renfe (thank you to Harold, who posted this a long time ago):
Buying Renfe Tickets Online

I second the recommendation to take the bus between Sevilla and Granada. The current construction on the train line into Granada means you have to transfer from the train to a bus at Antequera, so it is simpler if you have mobility challenges to just stay on one bus from start to finish. The ALSA bus was comfortable, cheap, and easy, and it didn't take any longer than the train.

Have a great time on your trip!

Before you go any further, I'd recommend you follow the earlier advice and read through this

https://www.seat61.com/Spain-trains.htm

You'll find it answers many questions and points you in the right direction for others. Really, this should be your starting point for Spanish trains. Note that buying from Renfe is his 4th option and the comment about Renfe not being good at showing changes which is relevant for Toledo-Madrid-Sevilla.

If your wife can travel on the bus Seville to Granada, it saves a vehicle change which the jncomplete train route requires....however, in Seville, that bus station is further away than the train station wherenyou would pick up your Renfe option. The town metro does run right by the bus station as your connecter.
I had an hour and 30 minutes between arriving from Cordoba to leave to Toledo which is too much time, but the 25 minute alternative was too short. There are waiting rooms and a small cafe for lunch or snack.

So when is the new timeline for the Seville-Granada high speed rail? A couple of years ago, the papers were saying by 2018 but obviously that's not happening. Anyone read any updates?

The Granada to Antequera engineering work was completed in 2017. However the railway failed the testing due to the computing systems not working and it is not clear when this will be sorted out.

The original plan was for this to be only phase one of an Andalucia link that would go east from Granada to Almeria and then further east to Murcia, eventually linking to Alacant. The other part would go west from Antequera to Sevilla then onto Huelva and then to Portugal. Who knows when/if any of that will happen.