Whitley's health had declined after she recently had several strokes, Raleigh Porter, 83, confirmed to the Associated Press.
"He loved her very much," Raleigh Porter said. "I think he just reached a breaking point."
Clarence Porter never married and Whitley's husband died several years ago, Raleigh Porter told the Associated Press.
"They had come in this morning just before Sunday school,” said the pastor, the Rev. Tim Brogan. “I’m still kind of processing everything.”
Brogan said the siblings had attended the 140-member church “a long time,” long preceding his four-year tenure as pastor.
He noted that the two had left behind brother Raleigh and his wife.
“We tried to find a way to comfort them,” Brogan said after learning the news.
The pastor preached a sermon about hope, but said it was difficult for church members to get through the day.
“Obviously, the mood was kind of down,” Brogan said. "We talk about this church being like a family."
Reporter Marcus Garner contributed to this report.