Lisbon to Marbella is 700km. ViaMichelin show a transit time of 7 hours on the shortest motorway route via Faro, Huelva, Seville, Jerez, Cadiz and Malaga . Consequently one has to accept that one will effectively lose one day en route and one day on return.
Also be aware that if travelling through the Alentejo and Andalucia between late May and early October it will be very hot with temperatures up to +-40ºC. One should therefore hire a car with aircon or else plan to leave early circa 04:00. and try to finish driving for the day by 11:00.
Note also that many car hire firms in Portugal charge extra for taking a rental vehicle into Spain. This should be verified when booking.
From personal experience I believe that this itinerary is very tight for one week of travel. More time will be spent in the car than elsewhere.
Seville itself really needs a minimum of 2 days to properly visit the Alcazar, the Cathedral and enjoy its ambiance. Lisbon probably needs at least 3 full days if one is going to do the basics of Castelo São Jorge, Belem, Jeronimos, Linha da Cascais (Estoril/Cascais) & Sintra.
For a week's trip I would counsel
a) Lisbon and Seville only
or
b) Seville or Granada and Marbella only.
