Even though it’s fiction, Marley’s ghost is in pain & chains and he warns Scrooge to repent.

(I have seen movies but never read the book which is unusual for me. I wonder if there is an edition written in its original version. )

The other stories are scary too.  They are meant if anything to warn us all to repent for our sins and grow in our faith.

Perhaps, but they should be exposed as ficition.  Too many people have been taken in by these fanciful narratives, and they do often carry a theological message with them, here the impostor Paul VI theory.  We have all those people at Palmar who got duped and led into joining a schismatic sect.

A Christmas Carol by C. Dickens IS a fictional tale, part of the English tradition of telling ghost stories on Christmas Eve. That is weird to say the least. Although a Christmas Carol is staple to watch (and the Alistair Sim version in THE version above all others - side note - Alistair Sim lent his voice to an abridged animated version of the same tale, released in the early 70s. The animation style is haunting, and worth viewing) for the Yuletide season, it is theologically incorrect. Dickens was not a Catholic, for starters. 
It would be interesting if there was a Catholic writer at the time who would have approached the same subject matter, but in light of Catholic persecution and discrimination at the time, I proffer that it would not have been published, let alone successful.

Marley was seen to by an Anglican priest and receive last rites in the Anglican Church, and based at least on the movie, he was repentant - to what degree we know not - but he already was trying to warn Scrooge to turn from his present course lest he suffer the same fate. This would illustrate most clearly in my mind the ineffectiveness of anything pertaining to Anglicanism. No real sacraments, so no real opportunity for the hope of salvation. That Marley would come back as a ghost I see as more in line with the ghost story tradition aforementioned.

Let us enjoy A Christmas for the literary and cinematic treasure that it is.  

As an aside...Shakespeare's Hamlet. We have an issue with Hamlet's father's spirit. There is also the quote that no spirit dare go abroad on Christmas Eve because of the holiness of that night. I thought to myself, what about Easter? Is Shakespeare tapping into the English tradition of ghost tales? is he trying to be careful not to avoid revealing his Catholicism? Is all of this just a literary construct without the view of being theologically correct? Again, the whole literature does not equate theology rhubarb.

(Damned souls possessing humans - premise behind The Conjuring movie, with the Warrens of paranormal fame. Much to confuse those who do not know what the Church actually teaches.)