The alternatives are limited at that time of night as the Aerobus to downtown will have stopped running. If you are incoming on a long-haul and are on a non-EU passport you may not get clear of the airport till mid-night.
The last metro trains leave each terminal at 01:00 BUT you will need to change from the Red Line (linha vermelha) to the green line (linha verde) at Alameda.
As there is more than one of you it might be better to take a taxi. However, and a BIG however, make sure the taxi driver switches on his meter before he even starts to move. Any argument, call one of the policeman who are usually around the taxi rank. There will be extras for bags and late night supplement but I would expect that a max. of +-€ 15.00 should get you to Baixa Chiado in a cab.
