Two nights is really, really inadequate for Seville. I'd hope for four. Add a night if you want to take a day-trip to Cordoba (which is orth at least two nights if you decide to forego Barcelona).
I urge you to reconsider the southern destinations if there is any hope you can return to Spain at a more pleasant time of year. Living in Florida (with, I assume, air conditioned houses, cars, stores and places of work) just is not the same as being a tourist in Andalucia in the summer unless you are gardeners by profession, or something like that. Madrid is also very hot. Barcelona will be somewhat cooler, but it can be humid, and you know what that means.
The website timeanddate.com has actual, historical, day-by-day weather data for most places tourist might go. I recommend checking out the last few years' data for July. Here's Seville for this year:
https://www.timeanddate.com/weather/spain/sevilla/historic?month=7&year=2022
There were just two days the entire month when the high temperature didn't reach at least 90 F. There were eight days with highs in the 90s. On 21 days the temperature reached at least 100 F (on three of which it hit 111 F).
I spent considerable time in Sicily and Puglia during the summer of 2015. Those areas aren't usually quite as hot as Andalucia. The heat was exhausting. You just can't be as energetic when you're wilting, so you cannot accomplish as much each day.
The northern strip of Spain from the Pyrenees across to Galicia is the best part of the country to visit in the summer. If you stick primarily to high-altitude spots and areas near m the coast, you should have very few really hot days.