The suspect, 57-year-old Jeremiah Fogle, killed one person at a home about a block away from the church before shooting the pastors, the Polk County Sheriff's office said.
The two men, pastor William Boss and associate pastor Carl Stewart, were in critical condition. No other church members were hurt.
Maria Beauford said the slain woman was her sister, 56-year-old Theresa Fogle. The Fogles married in 2002 and ran a transportation business together. They had been members of Greater Faith Christian Center Church, where the shootings happened, but had started their own ministry out of their house and regularly hosted Sunday services, Beauford said.
Beauford said she had never known Jeremiah Fogle to be violent toward her sister. He had been sick over the past year and had back surgery, and Theresa Fogle nursed him back to health, Beauford said. She said her brother-in-law was always smiling at family gatherings.
"We have no idea what his motive was," she said. "We just have no idea."
Jeremiah Fogle's older brother, Collis Fogle Jr, said that the couple never had a big wedding celebration and that they seemed to have gotten along well."It's so sad," Collis Fogle said. "I've been trying to call to figure out what went wrong.