At MK they are :
By Stitch's Great Escape
Buzz Lighthear Ride (to the side of the FP queue), these kiosks can be closed early or if quiet.
Frontierland - the path that connects to adventureland where the restroom are (?)
Outside Jungle Cruise - if you can, try using the kiosks here as they are always the quietest
Fantasyland - to the right of Philharmagic
As for backups, if one of the kiosks goes down, normally one of the cms there will stand in front of it and will use their tablet device