Perhaps there's a family member, like a grandparent, who tells stories about the secret pool. And then there could be a child who is curious and sets out to uncover the truth about the pool. There might also be a local who warns the characters about the pool for some reason.
Well, I think family could be a theme. In many short story collections, there are often tales that revolve around family relationships. Also, nature could be a theme considering the mention of a pool which is a part of nature. The stories might explore how characters interact with nature.
I don't know for sure as I haven't read it. It could be the popular kids at the school, or the swim team members.
In 'The Secret Sharer', the captain is a main character. He is the one who has the encounter with Leggatt, the secret sharer. There are also the crew members on the ship, who play important roles in the overall atmosphere of the story.
I'm not sure exactly who the main characters are without more information about 'The Secret Stories'. But usually in such stories, there could be a curious protagonist, someone who is eager to uncover the secrets.
Maybe an old wise figure, like an old man or woman who knows the secrets behind the door or has some knowledge about the events in the other stories. They could guide the younger characters or be a source of mystery themselves. For example, they might have a past connection to the secret door that is gradually revealed throughout the stories.
Since I haven't read the 'the drowning pool novel', it's hard to say for sure. However, in a story like this, there could be a detective - like character as one of the main characters. This person would be the one investigating any strange happenings around the drowning pool. There might also be a local resident who has some secrets related to the pool and becomes an important part of the story. And of course, there could be other characters who are either victims or bystanders that are affected by the events around the pool.
Since I don't know the exact 'Black Pool Story', I can't say for sure who the main characters are.
Since it's a novel about the dark pool, the main characters might include some shrewd financial wizards. There could be a young and ambitious trader who is trying to make a name for himself in the dark pool trading. There might also be an old - timer who has seen it all in the financial underworld and acts as a sort of mentor or antagonist. And perhaps a journalist who is trying to expose the secrets of the dark pool, adding an element of investigation to the story.
Often, the main character is an animal - lover. For example, a lonely old man who lives alone and finds comfort in secretly feeding the squirrels in the park. He becomes like a guardian for the squirrels.
I'm not sure specifically as the title doesn't give clear indication. But they could be ordinary people who are thrust into extraordinary situations where they encounter the secret miracles.