There are a number of podcasts on the four double homicides. I just found another set of podcasts when I searched google just now, about to listen to Unsolved "Colonial Parkway Murders part 1". There are at least four episodes about the Colonial Parkway on that show, each approx. 20 minutes. There are also the ones on the True Crime Garage called "Colonial Parkway Murder's" which was shared on this thread earlier. Plus Murder in My Family and a few more listed on wikipedia:
Colonial Parkway Murders - Wikipedia
"In January and February 2017, the "Shattered Lives" podcast featured two episodes with Parkway victim's siblings Bill Thomas, Joyce Call and Jennifer Phelps discussing the 30th Anniversary of the Colonial Parkway Murders and the status of the investigation.
In September 2017, the True Crime Critique podcast with host Jeremy Ryan welcomed Colonial Parkway Murders brother and advocate Bill Thomas.
On May 4, 2018, the Colonial Parkway Murders were featured in a live panel discussion at CrimeCon 2018 in Nashville, TN with former FBI agent Maureen O'Connell moderating a panel with true crime author Blaine Pardoe, and victim siblings and advocates Joyce Call Canada and Bill Thomas.
On July 7, 2018, The Murder In My Family podcast launched with host Mike Morford and guest Bill Thomas discussing Cathy Thomas and the Colonial Parkway Murders.
On July 24–25, 2018, the True Crime Garage podcast discussed the Colonial Parkway Murders in a two-part feature."