Mother-of-two Samantha Pithie, 32, died in the blaze at the Girl Talk sauna in Bexley Mount, Harehills, in the early hours of September 1 last year.
Karindu Fray, 25, and Darren Phelan, 30 – both of Scott Hall Avenue, Buslingthorpe – pleaded guilty to manslaughter before a trial was due to get under way at Leeds Crown Court this week.
Michelle McCormack, 32, of Claremont Road, Headingley, previously pleaded guilty to manslaughter.
A fourth defendant, Carol Banks, 31, of Thornfield Court, Cross Gates, previously admitted conspiracy to commit arson being reckless as to whether life was endangered and perverting the course of justice.
Sauna receptionist Mrs Pithie, pictured, who leaves husband Christian, 32, and a 13-year-old daughter Coral and son, Jordan, is understood to have died from the effects of smoke inhalation.
Police said the fire was started half-way up a set of stairs.
Detectives from West Yorkshire Police's Homicide and Major Enquiry Team launched an investigation after Mrs Pithie's body was recovered from the attic of the sauna.
Mrs Pithie, of Cardinal Grove, Beeston, Leeds, had decided to stay overnight instead of making the journey to her home on the far side of Leeds after the sauna had closed.
Terrified
Following the tragedy Mrs Pithie's husband Christian said: "She was terrified of walking through the Harehills area after finishing work at 10pm. She did not want to waste money on taxis and the sauna owner had agreed she could stay overnight. It was the first night she had done it."
People living near the sauna said it was open 24 hours a day. It is believed to have been divided into two parts, one for gay and the other for straight clients and had around 40 customers a day.
Fray, Phelan, McCormack and Banks will be sentenced on a date yet to be fixed.