This story involves one man and his grandpa who is called Gremper and a bunch of robots fighting alien invaders, they lead the aliens to believe the earth is inhabited by ghosts. The story is adventurous and fun but I can not remember the name of the book. Does anyone remember this book, I would like to know the name and who wrote it?
That's Sleeping Planet by William Burkett. It appeared in Analog (Serial: July-September 1964) and then in several paperback editions.
Humanity is the slight underdog in a war with an alien race. The aliens discover a plant whose pollen puts humans into a safe, reversible long-term sleep. They use it on Earth. The only people unaffected are a handful of humans who were on the alien planet the pollen comes from before the war started and became immune.
One of them -- Donnovan -- is captured and spends his time trying to scare his guards with stories about how his grandfather's ghost will get them. The guards mishear "Gremper," and Donovan does not correct them.
Another Immune, Daniel Rierson, is captured by robots and taken to their "master brain." Their master-brain (like all of them) is part of Earth's civil defense network which is prepared to act, but can't without human supervision.
They have a problem -- billions of human hostages -- so they try to act by indirection. They hear the rumors among the alien soldiers about Gremper (robots are everywhere) and decide to play that game. They make Gremper real and scare the aliens pretty badly...but their real purpose is to get into a Planetary Defense Center and wake the command staff.
It was a surprisingly good novel -- very much a newer take on Plus X / The Space Willies.