I would estimate Faro to Seville by car, dependent on traffic on the roads out of Faro, and on the approaches to Seville at 2hrs to 2hrs:15mins.
I have done Lagos to Seville non-stop in 2hrs 35mins.
Be aware that the approaches and entry to Seville itself can be a bit of a nightmare for the uninitiated and that it is very difficult to drive in the centre of the city.
For the centre, much better to park the car at somewhere like Colon in the underground car park and walk/bus it from there.
For return car hire into Spain from Faro airport, try Luzcar - www.luzcar.com. They do not charge for taking cars over the border to Spain.
Alternatively, for one way Faro Airport to Seville try the following guys, who I now understand are again able to offer one ways from Faro Airport to Seville, after the summer's capers.
http://www.iberiacarhire.com/
