Who  are the spirits ?  The Bible says in Luke chapter  16  verse 22  And it came to pass, that the beggar died, and was carried by the angeles into Abraham's bosom; the rich man also died, and was buried; verse 23 And in hell he lifted up his eyes, being in torments, and seeth Abraham afar off, and Lazarus his bosom.  verse 24  And he cried and said Father Abraham, have mercy on me and send Lazarus, that he may dip the tip of his finger in water, and cool my tongue; for I am tormented in this flame.  verse 25 But Abraham said, Son remember that thou in thy lifetime receivedst thy good things, and likewise Lazarus evil things: but now he is comforted, and thou art tormented.

Hebrews 9 : 27 And it is appointed unto men once to die, but after this the judgment.   Nobody comes back.

People go to Heaven or Hell according to the Bible .  So who are the spirits that are appearing as humans ?  They are  Demons.   The Bible says in  Second Corinthians Chapter 11 verse 14 And no marvel; for Satan himself is transformed into an angel of light. His demons can appear as angeles of light as well.  Demons will appear as familiar spirits.  Familiar Spirits are spirits that give an appearance of a person that is familiar to a human being.  For example : Demons know the history of the property and the person, so they can take on their appearance  of any person , so you will be interested in talking to them. 

We are not to talk to any spirits. Because the Bible says In Deuteronomy 18 : 9 - 12 that we are not to communicate with the dead. Nor are we to contact mediums or Psychics, Ghost Hunters or Ghost Investigators to help us contact or detect the spirits.