Cheryl Pepsii Riley goes by Pepsii.
James Whitcomb Riley went by The Hoosier Poet.
Cherlyn Schaefer goes by Sissy, and Sis.
Xianling Chen goes by Stella.
No.
You can use the vs seeker or go to the survival area restaurant after you have done the stark mountain side quest to rebattle gym leaders or Marley, Riley, Cheryl and Buck. 2-4 of them will be there and they change every day.
Riley Keough goes by Riley.
Reese Riley goes by Riley.
Aurelia Riley goes by Relie Riley.
Cheryl Kurn goes by Cher.
Cheryl Rusa goes by Lightning.
Cheryl Katz goes by Katz.
Cheryl Kenan goes by Sheri.
Cheryl Holliday goes by Phred.
Cheryl Fall goes by Cici.
Cheryl Gamble goes by Coko.
Cheryl Cosenza goes by Cher.
Cheryl Cornelius goes by Chere.