As regards Lisbon - Seville, this is a bit problematical. There are no direct train links.
TAP - Air Portugal currently have a daily one hour flight - Lisbon to Seville. Return prices this week are in the order of € 220 including taxes. Note One way tickets for this period are € 309! It may be cheaper to buy a return ticket rather than a one way and not use the return sector.
You would have to take the train from Sintra to Cacem, change to a train for Gare Oriente and then take a taxi five minutes to the Airport.
The alternative is long distance coach.
There is a twice daily service operated by www.alsa.es from Lisbon Sete Rios Coach Station to Seville Plaza das Armas.
If you go to my blog at
http://barlaventostravelblog.blogspot.com/2008/03/sintra-seville.html
you will find a copy of this reply together with a png image of the current timetable for the service. Click on it to view and download.
You would have to take the train from Sintra to Cacem, change to a train for Sete Rios go the ground floor and walk over to the Bus Station.
Hope this helps.
