Rome to Lake Como then Spain

It seems you're talking about 2 nights (1 day) in Rome, 1 night (a few hours) in the Cinque Terre, 1 night (a few hours) on Lake Como, and then head to a hotel near either Malpensa or Linate Airport for a night. Or if the flight(s) depart reasonably late in the day, you could spend two nights on Lake Como.

That seems to amount to a lot of driving or train time, plus checking in and out of at least 3 hotels, by comparison to not much sightseeing time at all.

I think you'll find that driving from Milan to Seville is not a practical option. ViaMichelin estimates the driving time at 19-20 hours with no stopping, getting lost, looking for parking, detouring to towns, etc. Fuel and tolls will cost about $400, and there's the not-minor matter of the international drop charge for leaving an Italian car in Spain. That fee will almost certainly be in the hundreds of euros. Rome alone is easily worth five nights.

Reality check indeed. I agree with acraven that you are trying to visit too many places. Way too many. And you won't be able to enjoy much when half your days are spent checking out of one hotel, riding a train, and then getting to and checking into your next hotel. I think you need to discuss amongst yourselves which places get put on the shelf for your next trip.

Driving to Spain should be your last option, for the reasons already given. But you could train to one or two places between Milan and Seville. Or just fly to somewhere in Spain and work your way to Seville.

Agree with acraven. So much driving in so little time.

Seeing the Pantheon takes at most an hour. There is plenty to do in Rome.

Since you have to end in Milan, suggest 3 days in Rome, 2 in Lake Como. Or 2 nights in Rome, 1 in CT. I am not sure the reason you want to cover so much territory so quickly.

Milan to Seville is a huge distance. Consider a flight to give you more time in Italy

Not clear-

How will you travel thru Tuscany to Lake Como? Car? train?
Are you renting a car and thinking of dropping in Spain? If so, yikes.

If you have just 1 week between Milan and Seville I'd do no more than 2 stops between. 3-4 nights each- Barcelona? Valencia?
Will you have more time in Seville and surrounds once you get here? If not then just fly to Seville and use the week to tour that area. As long as you are not interested in more of Italy.

The Pantheon will not even take an hour. Why just that?

I agree, the pantheon takes, 1 hour tops. There are interesting churches close, Sant' Ignazio and Gesu. Unfortunately, we were really looking forward to seeing Santa Maria Sopra Minerva right next to the Pantheon and its closed indefinitely. (we were there 11/2019). Relatively close to the Pantheon is the Piazza Navona, which has a beautiful fountain and likely a huge crowd. Still we enjoyed being there.

On our recent trip we visited both Lake Como and Cinque Terre (October 2019). Even mid October CT was very crowded. The weather wasn't great, and those two locations are very weather dependent. Your short stays are risky, IMO. If you get bad weather like we did, given your short stays, I can't imagine you'd be able experience much. If it were me, I'd look at a longer stay in Tuscany. Perhaps a couple nights in Siena and a couple more in a smaller town. Or, maybe this thread on Turin would peak your interest. It's relatively close to Milan.

https://community.ricksteves.com/travel-forum/italy/turin-bbf4f20b-936b-4cf7-8768-27a56c9762c8

In terms of driving from Milan to Sevilla. That sounds stressful and exhausting. You would be crossing several borders and I would imagine that would be an expensive rental. I guess I'd fly from Milan to Sevilla. Or fly from Milan to Barcelona to experience that city and then train to Sevilla (which still would be a long ride). Sevilla is a great city with plenty to experience.

Definitely flying or taking the train to get to Seville. Appreciate the perspective regarding not trying to see too much in one visit. Any suggestions for a particularly stellar village in Tuscany in which to visit for a few days, hang out and tour the area?

Lake Como or Cinque Terre?

Better to fly to/from Seville, Spain to/from Florence, Milan or Rome?

Use a website like Google flights to check schedules and fares for Italy-Spain and Spain-Italy. Fares are highly specific to origin, destination and date. From my origin, the two cheapest options in Spain (by far) are Madrid and Barcelona. In Italy, Milan and Rome are the least expensive. It may be different for you. Price out Multi-city tickets both ways.

If you decide to fly between Italy and Spain or vice versa, handle that flight separately from your transatlantic trips. I use skyscanner.com to research flight options within Europe.

Still unclear exactly what you want to do.
As I read your original post you have 5 nights in Italy with your daughter. Meeting in Rome for 1 night- then you have 4 nights left. You will need to be in your departure city the night before your flight to Spain (or your daughter's flight- has she already booked that?)
That means 3 nights to spend somewhere - you mention Tuscany, CT and Lake Como. It's just not feasible to do more than 1 of those locations given your time constraints.

Tuscany- our favorite town was Montepulciano- you would need a car here or else you are dependent on bus travel/private driver to any other locations.
Florence would make the most sense as you have many transportation options for day trips and it has an airport from where you could fly to Spain (or wherever your next destination is). Siena might work as well but keep that last night before departure in mind.
I have not been to CT or Lake Como so can't comment- although CT does require a bit more effort to get there

If you haven't yet please pick up some good guide books and a map.

TBH- with just 5 nights- I'd stay in Rome- unless you have been before? Still puzzled as to why Pantheon is only sight you want to see.