The 2 of us had planned to fly into BCN in early May, spend a night near BCN Sants, and take a train to Seville (returning to stay in BCN the following week after several nights in Sevilla and Granada). But at this point, the train tickets I'm seeing on trainline.com are more than double the airline tickets, and most of the train trips involve 6-8 hours and one change. (We won't be able to do the early morning direct train). So am rethinking - maybe we should just stay near the airport that one night and fly? I know flying takes time but a 1 hr 45 min flight vs a 7 1/2 train is substantial. Would prefer the train both for the environment and to see a bit more of the countryside, but not sure now. Thanks for any advice!
Flying is probably the more practical option to travel between the two cities. If you do book a flight for the next day I wouldn't stay near the airport that first night in Barcelona- go into town and enjoy it. Then back to the airport for a late morning/early afternoon flight.
Re trains: I don't know what Trainline sells, but if they don't have the Iryo trains, you might want to look at them. You could also maybe split the journey, and spend the first night in Madrid.
*edit to add- It looks like Iryo won't sell a connecting ticket. You'd have to book Barcelona-Madrid and Madrid Sevilla separately. And in that case, you could price-shop the legs separately.