The indictment charges the nanny with causing the death of Leo and Lucia Krim.
Ortega, 50, was hospitalized from self-inflicted stab wounds, including a deep gash to her throat.
Police said Marina Krim, the Manhattan mother who employed Ortega, returned to her Upper West Side apartment Thursday to find two of her children, ages 2 and 6, dead of knife wounds and the nanny stabbing herself with the blade.
"Apparently over the last month she was not herself," said police department spokesman Paul Browne.
But relatives in Ortega's native Dominican Republic said they were shocked by the allegations.
Miladys Ortega, the nanny's older sister in the Caribbean nation, told The Associated Press that her sister "loved those children." She said the family felt the nanny was "unable to do that."
She said Yoselyn is the youngest of six siblings, most of whom live in the United States. Her sister emigrated to the United States in the early 1980s after graduating from accounting studies at Santa Ana College in Santiago.
Yoselyn Ortega worked as the manager of a print shop in Manhattan, until she separated from the father of her child. She returned to Santiago for a while, but then went back to the U.S., her sister said.
Miladys Ortega said that when her sister got back to New York, she couldn't find an accounting job and decided to work as a nanny because she loves children.
During her last conversations with Yoselyn, her sister didn't say anything that seemed unusual.
"Yoselyn always was a normal person. When she was a child, she played, always played a lot. We would go into the countryside," she said. "As an adult, she dedicated herself to working. She was always working."
Juan Pozo, a 67-year-old car service driver who formerly rented a room from the Ortega family, told The New York Times that the nanny's sister told him Friday that she had "felt like she was losing her mind" lately, and had recently been taken by relatives to visit a psychologist.
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