The defectors in the court filings had said that Iranian officials had "foreknowledge of the 9/11 attacks", The New York Times reported.
The suit, filed in Manhattan court, contends that Iran and Hezbollah, the Lebanese militant organisation with close ties to Tehran, helped al Qaeda in planning the attacks on September 11, 2001, and in facilitating the hijackers' training and travel.
After the attacks, Iran and Hezbollah helped Qaeda operatives escape, providing some with a safe haven in Iran. the suit contends.
The question of an Iranian connection to 9/11 was raised by the national 9/11 commission and has long been debated. Al Qaeda, which adheres to a radical Sunni theology, routinely denounces the Shiite sect that holds power in Iran, and the terrorist network's branch in Iraq has often made Shiites targets of bombings, the Times said.
But, intelligence officials have long believed there has been limited, wary cooperation between al Qaeda and Iran against the United States as a common enemy.
The lawsuit also names as defendants Iranian officials and ministries, Hezbollah and al Qaeda, among others.
The families' lawyers have asked for a default judgment against the defendants, which have not mounted a defense. Even if there were such a judgment, legal experts say it would not be easy to collect monetary damages.
The names of the defectors were not in the court filings but were submitted to the judge under seal, the Times said.
The Times cited the 9/11 commission report as saying that there was "strong evidence that Iran facilitated the transit of Al Qaeda members into and out of Afghanistan before 9/11, and that some of these were future 9/11 hijackers."
But the commission said that it had "found no evidence that Iran or Hezbollah was aware of the planning for what later became the 9/11 attack," and that the "topic requires further investigation by the US government."
