There's no way to know the main characters without more information about this novel. However, in a novel with such a title, you would expect the 'other man' to be central. There might also be a female character if it's a love - related story, or another male character if it's about male - male relationships like friendship or competition.
I really can't determine the main characters of 'the other man novel' without reading it. But it could be that the main character is a person who is haunted or influenced by the presence of the 'other man'. There might be other supporting characters like family members or friends who help to flesh out the story and show how the relationship with the 'other man' affects the main character's life.
In a more general sense, the main characters in the 'the other man story' could be the 'other man' and the people or group that he is trying to infiltrate or be a part of. For example, if it's a story about a new employee (the other man) in an office, the other main characters could be his colleagues, his boss, or the people he is replacing. Their reactions to him and his actions towards them would form the core of the story.
I'm not sure specifically as I haven't read it in detail. But I assume the 'Jealousy Man' is one of the main characters. There may be others who are related to him in some way, like friends or family members who are affected by his jealousy.
I'm not entirely sure without having read it in detail, but likely there are characters that represent different aspects of the society depicted in the book. Maybe there is a push man who could be central, perhaps someone who is constantly in a position of having to push forward in a difficult life.
I'm not entirely sure without reading it specifically, but typically in such a work, there would likely be an ordinary man as one of the main characters, and then perhaps a character representing the superman. There could also be supporting characters like friends, family, or antagonists.
Artaban is the central figure. He's a wise man with great knowledge and resources. Along his journey, he encounters different people. There are the people he gives his gifts to, like the girl who was sold into slavery. And then there are those who are part of the historical and cultural context of the story, such as the merchants and the people in the towns he passes through. All these characters play a role in shaping Artaban's story and his understanding of his quest.
The man upstairs is likely one of the main characters. But without reading it, it's hard to say who else exactly.
The main character is clearly the man with the scar. But there might be other supporting characters who interact with him and whose stories are also told in relation to his. Maybe a friend or a family member who has a different perspective on the man with the scar.
The Gingerbread Man is obviously a main character. And often there are animals like the fox, the cow, and the horse who are also important as they are the ones chasing the Gingerbread Man.
Since it's a collection of stories, there are likely to be multiple main characters across the different tales. In the story 'The Third Man', perhaps there is a character who discovers the presence of the third man, and this discovery drives the plot. In other stories, there could be characters who are dealing with personal problems or are involved in some sort of intrigue.
The Donkey Man is surely a main character. He might be accompanied by his donkey, which could also be considered as an important character in a way. There may also be characters such as the villagers or townspeople who interact with the Donkey Man. They could play important roles in the stories, for example, some might be his friends, some his foes, and others just bystanders whose lives cross paths with the Donkey Man's.