I do not think what you are experiencing is your grandfather. You and he were close and you cared about each other very much. He would not do anything to frighten you.
I don't think you should visit a spiritualist again. Instead, try to find someone you can speak with who will look at things realistically and try to help you to see things from a different point of view; maybe they will be able to give you some rational explanations that will help put your mind at ease. You aren't crazy.
There are many different types of hauntings that have been researched. People can believe what they want, but no one can dismiss YOUR experiences. I consider myself a logical and reasonable person, but I have seen enough unexplained things and had enough strange experiences (many of them shared with other "logical" people) that I can say without a doubt that yes, I believe ghosts are real.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.