Four.
" After being warned by Marley's ghost to change his ways, Scrooge is visited by three ghosts – each in its turn – who accompany him to various scenes with the hope of achieving his transformation."
I have watched the 1951 version staring Alastair Sim many times. A superb adaptation, still considered by many to be the best. There is a scene in which Scrooge is shown a homeless woman with a baby huddled in a street. They are surrounded by a large number of spirits (ghosts) who are reaching out to them but seem powerless to help.
I could not find the above mentioned scene but here is the redemption scene which is wonderful.
https://en.wikipedia.org/wiki/A_Christmas_Carol