Diane Staudte , 51, of Springfield was charged on Friday with two counts of first-degree murder, one count of first-degree assault and one count of armed criminal action.
Authorities say the 51-year-old allegedly killed her husband and son and attempted to kill her daughter.
Her 21-year-old daughter, Rachel, was charged with the same counts Saturday.
Police say the women confessed to putting antifreeze in their family members' soda and Gatorade over several days.
When questioned by detectives, Diane admitted she had killed her husband because she "hated him" and her son because he was "worse than a pest".
She said she wanted to kill her daughter, Sarah, because the young woman "would not get a job and had student loans that had to be paid," the probable cause statement said.
The medical examiner in Greene County initially ruled that the husband had died of natural causes and the son as a result of prior medical issues. Authorities re-examined the deaths earlier this month after Diane Staudte's 24-year-old daughter, Sarah, was hospitalized.
A detective wrote that a nurse told him that although Sarah Staudte's condition was potentially fatal, Diane Staudte had visited only a couple times and not stayed long. The nurse described Diane Staudte's actions as "inappropriate," saying she joked and laughed with hospital personnel.
The nurse also told the detective that Diane Staudte told her that she planned to go on an upcoming vacation to Florida regardless of her daughter's status.
Sarah Staudte remains hospitalized in intensive care.
Diane and Rachel Staudte are being held without bond. If convicted, they could face the death penalty.
The Associated Press contributed to this report.
