Travelling between cities in Italy and Spain

Between Barcelona and Granada: Fly
Between Granada and Sevilla: ALSA Bus
Between Sevilla and Madrid: AVE high speed train

Make sure to stop at Cordoba for a few hours (on the same rail-line between Sevilla and Madrid) to check out the Mezquita de Cordoba, one of the top 5 sights of Spain.

No need for a Eurail pass this trip I recommend this site for advanced (like book them now) train tickets in Italy (as it list all both Trenitalia and ItaloTren trains) and also Spain https://www.thetrainline.com/?redirected=true

I like the ALSA bus also as I used it about two months ago to go between Granada and Seville
https://www.alsa.com/en/web/bus/home

Looking at your itinerary I would book tourist sites piecemeal and decide if you want a guide at each.
If you are trying to go to the Alhambra you might want to look at booking those today if they are still available.

Wow, you are going to need a holiday to recover from this pace with only one full day in most places!

You are arriving over Easter weekend, so check what is closed. Most transport will be running reduced schedules.

One day in Rome? I'd skip Naples and Sorrento and add it to Rome.

Granada to Cordova to Seville. Don’t miss Córdoba and the Mezquita.

That itinerary is a real problem. You're going to spend a lot of money traveling to all of those places but not really seeing much. It will be absolutely exhausting--mentally as much as physically, because you're going to be thinking constantly about all the things you haven't been able to see in the current city as you're rushing to the train station, bus station or airport to get to the next one.

And if you don't already have tickets to the Alhambra it may be too late to get one from any source, in which case going to Granada on such a compressed trip is not a good idea. At this point your hotel in Granada may be the best place to look for tickets. If no luck there, it's down to paying $$$ for a tour. But be sure the tour includes the Nasrid Palaces. There's at least one company that has sold tickets to the "Alhambra" without making it clear that the top sight wasn't included.

That is an aggressive pace, and given it is your honeymoon ( per other post), looks more like an endurance test.

As others have already said, a rail pass is no benefit for where you are traveling.

What is a 'big rucksack', ( dimensions) ?

What size is the 'suitcase trolley'. Presumably you mean a wheeled bag?

Since everything is booked, just be sure you have a well defined list of what you are doing at each location.

Good luck

If you are a Senior ( it was over 62) you can buy a carte del oro for Spanish trains. Unlike other European countries, it was not expensive. In 2015 it cost 5 euros. We used just for the high speed from Seville to Madrid. The almost 40% discount made it well worth the cost. The agent in Seville did not volunteer discount info. even though my hair is all gray, you have to ask and then they will take care of you, hopefully. Buen viaje, Hank, Novato, Ca

I also think a more enjoyable trip would be fewer stops. Your itinerary would be possible on a guided tour, with a bus from hotel to hotel and a guide to lead you to the top spots without getting lost or waiting in line. But it's going to be very different on your own. Every time you move, you have to go door-to-door with your luggage, including packing time and travel to/from train stations. To go from Rome to Sorrento, you need a train to Naples, then transfer to the s.l.o.w. local Circumvesuviana train to Sorrento.

I would skip Milan, unless there is something really special you want to do there and continue by train to Venice, staying at least 3 nights. Venice to Florence is a couple hours by train, Florence to Rome a little less. Stay in Naples and day trip to Sorrento and anywhere else you want to see (there's a day's worth of sights in Naples plus the very excellent archaeology museum).

If you are going to Granada to see the Alhambra, do you have tickets yet? I hope so, since they are sold out for May.

I'll be watching the Inter Milan vs Roma game in Italy on the 20th.
Also haven't booked Alhambra tickets, what can I do now?

Thanks Scythian. I've booked all my trains using loco2.
Unfortunately my itinerary is set and hotel booking have been done. I can't change anything, but maybe your suggestions can help me plan my days accordingly.

Thanks Carlos,
I've booked ALSA bus from Granada to Sevilla. Got a 50% discount for some reason. So that was great as well.
Will try my best to visit Cordoba