Police of Tay Ninh detained Mai Thi Nho, 50, and her sister Mai Thi Tuyen, 43, on Thursday to be investigated for murder.
Authorities said that on Oct. 23, Nho began to show signs of delusions, saying that her deceased father had possessed her, and that her brother and his 2-year-old son were "bewitched."
Nho, in the name of her father, summoned 22 relatives at her mother's house in Trang Bang Town for an "exorcism."
Nho closed the doors and burned incense with her sister Tuyen, while asking everyone to kneel. During the "exorcism," Nho and Tuyen said demons appeared and asked everyone to cover themselves with sheets and lie on the floor.
Nho then said six people were possessed by demons, and needed to be exorcised.
She forced them to drink alcohol, consume oranges and eat burning incense while being beaten in the face and chest. Tuyen then danced while holding knives and slashing objects inside the house. Nho forbade family members from going outside, saying that doing so would result in re-possession.
At 10 a.m. the next day, the fracas was still going.
Nho said her brother and his 2-year-old son were possessed by demons again, so they were pinned to the ground to continue the "exorcism."
Authorities said that despite the father and son's pleas and cries for help, Nho and Tuyen only stopped once the victims had died. Family members then panicked, ran outside and reported the matter to the police. Nho and Tuyen were arrested afterwards.
An investigation is ongoing.