Yeah, there are definitely multiple panels interviewing that day. From the selection process info on the RTK site:
Each interview panel is chaired by a federal judge, and consists of a faculty member, distinguished alumni, and current Root-Tilden-Kern scholars. Based upon the recommendation of these panels, the program directors name the Root-Tilden-Kern scholars.
ETA: Also, I'm a little unclear. Is it 20 total, including all the named ones (D'Agostino, Jacobson, Sinsheimer, etc.) or is it 20 plain RTK + all of those ones?