Mediums, psychics, seances etc are all complete bull. It's pretty much common, there have even been numerous books, documentaries etc. on how it's done. Yet for some reason people still flock to circus shows by con artist like Derek Accorah and Psychic Sally. I know some people suffer very badly from the loss of a loved one, but it doesn't excuse them from complete idiocy. You might as well ask a tin of beans if you're loved one's are at peace.
As for ghosts. There's probably something in it, by way of science we cannot yet explain. Maybe when people die suddenly, violently and/or unexpectedly there is some form of weird energy released.