This may help. See the book "Saints and Sinners" by Lawrence Wright pub. 1993. I got it from the library.
There is a chapter on Jimmy Swaggart. He gives a history of Jimmy Lee Swaggart, and his two first-cousins Mickey Gilley and Jerry Lee Lewis. The book kindly explains their relationship.
According to Wright:
Jerry Lee Lewis "the Killer" of Rock & Roll fame, born September 29, 1935 in Ferriday, Louisiana, was the son of Mamie Calhoun and Elmo Lewis. Jerry Lee had a younger sister, Frankie Jean Lewis Terrell.
Jimmy Lee Swaggart, Defrocked Televangelist, was the son of Minnie Bell Calhoun and Willie Leon "Sun" Swaggart. His grandparents were Ada and Willie Harry Swaggart. Jimmy Lee Swaggart was only a few months older than his cousin, Jerry.Jimmy Lee Swaggart married Frances Anderson and they had a son named Donnie. Jimmy Swaggart wrote an autobiography (with Robert Paul Lamb) titled "To Cross a River".
Mickey Gilley, Country Singer and Pianist/Showman currently performing in Branson MO, was born 9 Mar 1936 in Mississippi, and was the son of Irene (Lewis or Calhoun?) and Arthur Gilley. His second wife was Vivian. Mickey had another wife in Texas named Geraldine Garrett.
Sisters Mamie and Minnie Bell Calhoun had a brother "Uncle Lee" Calhoun of Ferriday, LA for whom both Jerry Lee Lewis and Jimmy Lee Swaggart were named. How Mickey Gilley was their cousin is sadly not explained.But the three boys grew up together in Ferriday, LA.
BTW: There is a rumor that Ricky Lee Skaggs, of Bluegrass fame, born 18 Jul 1954 at Brushy Creek, KY (near Cordele KY) is also related to Mickey Gilley.Ricky Skaggs is the son of Dorothy and Hobert Skaggs.He married Sharon White on Aug 4, 1981 and they had a son named Andrew who was murdered prior to 1991.
I do not know the parents of Myra Gale Brown, Jerry's bass player's daughter.Myra was Jerry Lee Lewis' 3rd wife and his second cousin whom he married when she was only 13 years old. They had a child, Jerry Lee, Jr.
According to Wright, Jerry Lee Lewis had 6 wives.His First wife whom he married when he was 16 years old in 1952 was Dorothy Barton, who's father was a preacher.He was suspected of murdering his 5th wife, Shawn, who was found dead in Jerry's guest bedroom in 1983, but Jerry denies any involvement in her death.