Apparently, the contestants will consist of "superfans" teaming up with contestants from the shows in question.
Survivor:
Natalie Anderson, Season 29 winner
Joe Anglim, Seasons 30 and 31
Rupert Boneham, Seasons 7, 8, 20 and 27
Jeremy Collins, Seasons 29 and 31 (winner)
Cirie Fields, Seasons 12, 16 and 20
Woo Hwang, Seasons 28 and 31
Rob Mariano, Seasons 4, 8, 20 and 22 (winner)
Kelley Wentworth, Seasons 29 and 31
Tina Wesson, Seasons 2 (winner), 8 and 27
Big Brother:
Frankie Grande, Season 16
Britney Godwin, Seasons 12 and 14
James Huling , Season 17
Will Kirby, Seasons 2 (winner) and 7
Janelle Pierzina, Seasons 6, 7 and 14
Rachel Reilly, Seasons 12 and 13 (winner)
Da'Vonne Rogers, Season 17
Jeffrey Schroeder, Seasons 11 and 13
Ian Terry, Season 14 (winner)
The Amazing Race (competing as pairs):
Leo Temory and Jamal Zadaran, Seasons 23 and 24
Tyler Oakley and Korey Kuhl, Season 28
Erin Robinson and Joslyn Davis, Season 28
Joey Buttitta and Kelsey Gerckens, Season 27 (winners)
Natalie "Nat" Strand and Katherine "Kat" Chang, Season 17 (winners)
William "Bopper" Minton and Mark Jackson, Season 20
Tiffany Chantell Torres and Krista DeBono, Season 27
Brook Roberts and Claire Champlin, Season 17
Nathaniel "Big Easy" Lofton and Herbert "Flight Time" Lang, Seasons 15, 18 and 24
Source