Last remark before I resign.
I contacted my travel agency, AA & Iberia.
Travel agency : has no access to the seat maps, can't do anything.
AA : The agent told me she could book seats but they would charge a fee to take over the reservation as it wasn't made with them. 25usd per person.
Iberia : Told me they couldn't reserve seats as it was a codeshare with AA.

Here it stops, as Iberia is my return flight I will try my luck at the airport when I'm there for the outgoing flight.