Ramiro Santisteban and Jesus Tello told the judge on Monday they could not recognise the four men when shown 60-year-old pictures of them.
The two Spaniards were deported to the Mauthausen concentration camp in Nazi-occupied Austria from France, where they had fled after Spain's 1936-39 civil war.
They are among 7,200 Spaniards who were imprisoned in the camp during World War II, 4,300 of whom died.
Families of Spaniards deported to Nazi concentration camps filed the suit against four suspected former SS officers - Anton Tittjung, Josias Kumpf, Johann Leprich and John Demjanjuk.
Germany has also issued an arrest warrant for the Ukrainian-born Demjanjuk, who lives in the United States but who has been stripped of his American citizenship over his Nazi past.
Germany accuses him of taking part in the deaths of at least 29,000 Jews when he was a guard at the Sobibor Nazi concentration camp in what is now Poland from March until September 1943.
The Spanish lawsuit demands that the four men be extradited to Spain to stand trial for the deaths of Spanish citizens at camps at Flossenberg and Sachsenhausen in Germany and at Mauthausen where they allegedly worked as guards.
Spain's National Court accepted the suit last July under Spain's principle of "universal jurisdiction," with which crimes against humanity, war crimes, terrorism and other heinous offences can be prosecuted in Spain even if they were allegedly committed abroad.