AUSTIN — Two more families who lost loved ones in the Sutherland Springs massacre last year are suing the U.S. Air Force for negligence, doubling the number of legal challenges the government is facing over the mass shooting.

The Johnson and McNulty families filed their lawsuits this week. The Air Force admitted it failed to report veteran Devin P. Kelley's past crimes to the federal database, the suits state, which allowed him to pass a background check and obtain the firearms he used in the shooting.

The two families filed negligence claims earlier this year and were required to give the government six months to try to respond. Attorney Jamal Alsaffar said his clients got "nothing more than a cursory response" in that time, so they decided to sue once the deadline hit.

"The government has done nothing — literally nothing — to resolve the claims or help the families," Alsaffar told The Dallas Morning News on Thursday. "That's why we had to file the lawsuits because there was no effort made."

On Nov. 5, Kelley shot and killed 26 parishioners — including a pregnant woman — who were attending Sunday services at First Baptist Church of Sutherland Springs. Among the victims were Tara McNulty, 33, a mother of two, and Sara, 68, and Dennis Johnson Sr., 77.

Two other families sued the federal government earlier this year. They are Margarette Vidal, who survived after being shot in the knee and next to her spine, and Joe and Claryce Holcombe, who lost nine family members in the massacre. Their lawsuits have been consolidated, a step Alsaffar expects all of the families to take.

Due to the doctrine of sovereign immunity, it's usually almost impossible to sue the federal government. But under the Federal Tort Claims Act, people can seek damages in limited cases if they can prove direct negligence on the part of the government.

Kelley, an Air Force veteran, had a history of violence and mental illness. He received a bad-conduct discharge in 2014 after he was convicted of beating his first wife and assaulting his stepson, and he had escaped two years earlier from a mental facility where he was admitted after threatening to kill his superior officers. Normally, these incidents would have landed Kelley on the FBI's criminal database and kept him from legally owning guns.

But the Air Force failed to report his crimes, allowing Kelley to pass two background checks before he bought the Ruger AR-556 he used in the shooting.

In their lawsuit filed Wednesday, Dennis and Sara Johnson's children claim the government's admitted failures entitles them to damages for pain and suffering, mental anguish, mental health care expenses, past and future lost income and earning capacity and funeral costs.

No dollar figure is named in the lawsuit.

Several other victims of the shooting are also suing Academy Sports + Outdoors, where the shooter purchased his firearm. Kelley bought a Ruger and at least one high-capacity magazine there in violation of Colorado law, where he was a legal resident at the time, the lawsuit alleges.