Brian and mrs767er, thank you for the info and the offering to check the seat availability. I'll wait till we get closer to the date then.

My preference is for GIG-Anywhere, but if the chances might be higher in GRU or BSB, I can take the flight there. Right now, I'm putting the possibilities in this order:

Madrid is the best destination for me, as it's near enough Lisbon to go by train or bus and I could stay a few days there. Barcelona would be good enough, as it is easy to get to Madrid from there. As I said, BSB is an option, but more difficult than GIG or GRU.

1) GIG-ATL-MAD
2) GIG-ATL-BCN
3) GRU-ATL-MAD
3) GRU-JFK-MAD
4) GRU-ATL-BCN
4) GRU-JFK-BCN
5) BSB-ATL-MAD
5) BSB-ATL-BCN

If Spain wouldn't be an option (or at least a good one), I think that CDG ou AMS would be destinations to consider. I would have to buy a ticket to go from there to Lisbon, but the price is fair. I read a lot of people in this forum telling that CDG should be avoided, so, I'm thinking first of AMS.

Thank you all for the help.