A gentle correction is in order.
The angels and the saints, those who have gone before ahead of us, support us in this life not only by their prayers of intercession, but they can and do come to earth called “apparations”.
The only time a ghost is described in His word, it refers to giving up the ghost or the Holy Ghost.... whatever medium or soothsayer or Hollywood has told you, do not believe it.... believe His Word.
His word warns not to turn to mediums or spiritists for you will be defiled by them .. Leviticus 19 ..
I was under the assumption you are referring to saints as believers until you noted intercession.. Saint can have a more broad definition... especially for one Church that goes quite a ways to honor (worship) dead believers with feasts, days....
And if you are a member of that church with the likes of fatima, I can see completely why you believe what you believe....
There is NOTHING Scriptural about such "intercessions" of the dead or "saints".
Demons DO OFTEN appear as apparitions, masquerading as angels of light, even producing Marian visions and speeches.
Moreover, NO mortal can be reincarnated in this world to "help." That act is an intention deception by Satan. OTOH, the Lord Himself MAY and HAS interceded -- but without all the physical fanfare.