Tami Huntsman, 39, may face the death penalty, according to a news release from District Attorney Dean Flippo. Gonzolo Curiel, 17, cannot receive the death penalty because he's a minor, though he'll be tried as an adult. The complaint noted he was 16 when the alleged crimes occurred.
Huntsman is thought to be the aunt of the two dead children. Police identified them as Delylah Tara, 3, and her brother, Shaun Tara, 6.
Each defendant was charged with two counts of murder, three counts of torture, one count of child abuse and two counts of conspiracy -- one to commit torture and one to commit child abuse.
After police arrested Huntsman and Curiel, authorities learned that Delylah and Shaun were missing, authorities have said. Acting on information from the suspects, police looked inside a storage unit in Redding and found bodies of the two children stuffed into a plastic storage bin.
Flippo has said he thinks the killings and abuse of the 9-year-old happened in Salinas, in Monterey County, before Huntsman and Curiel moved to Quincy in early December.
The complaint says the killings and abuse happened on or around November 27.
Details of the alleged torture were not given, but the complaint said the couple caused "cruel and extreme pain and suffering for the purpose of revenge, extortion, persuasion and for a sadistic purpose."
The couple abused the 9-year-old by not properly clothing or feeding her, kicking and beating her, breaking her bones and not providing medical care, the complaint said. The girl has been hospitalized, authorities said.
Flippo said he'll decide whether to seek the death penalty against Huntsman after the preliminary hearing is completed.