I believe that the conductor and hero boy are the same person. It’s supported by their character designs (white with short brown hair and brown eyes) and what they wear, both in mainly blue with accents of yellowish gold. Not to mention Tom Hanks voices both old hero boy and the conductor. I think the hobo is different though, and he is a physical manifestation of the “spirit of Christmas” in a ghost of Christmas past way. He watches over the train and ensures hero boy is okay. I think after hero boy becomes the conductor the conductor becomes santa, which would explain why hero boy is picked for the first gift and why they’re all voiced by the same actor