There's no way to be sure without reading the story, but it could be a student who makes the mistake of getting in the wrong line.
It's possible that the main character is a shy student who is forced out of their comfort zone when they end up in the wrong lunch line. And there could be a bully or a friendly peer in that line who becomes an important part of the story as well. So, the main characters could include the shy student, the bully or friendly peer, and perhaps a cafeteria staff member who gets involved in the situation.
Maybe there's a cafeteria worker who notices the character in the wrong line and has an interesting reaction. So, the main characters could be the student and the cafeteria worker.
Well, it could be about a student who accidentally gets in the wrong lunch line. Maybe they end up with a completely different meal than they expected, and then all sorts of funny or interesting things happen because of that mistake.
I'm not sure as I haven't read the story. But usually, in a short story, there could be a protagonist who is directly involved with the red line concept. There might also be an antagonist who opposes or challenges whatever the red line represents.
The main characters in the 'life line short story' might be people who are facing some sort of crisis. It could be a doctor and a patient if the story is about a medical emergency where the doctor's actions are the patient's 'life line'. Or it could be a teacher and a student if the story is about how the teacher's guidance is the student's 'life line' in academic or personal growth.
Since I don't know the story, I can't say for sure. But it could be an ordinary person, like a worker who is at the end of his career, or a young person at the end of their adolescence.
Most likely, the main character is the lighthouse keeper himself. He is the central figure around whom the story of the lunch revolves.
Without knowing the particular 'end of the line story', it's difficult to name the main characters. But if it's a story about the end of a war, the main characters could be the soldiers on both sides. There might be a heroic soldier who has survived until the end of the war and is now facing the aftermath. There could also be the generals who are responsible for making the final decisions that led to the end of the conflict, and the civilians who are also affected by the end of the war in various ways.
The main character is the Lunch Lady herself. She's the one with the secret identity. There are also often students who play important roles, like sidekicks or those who get involved in the Lunch Lady's adventures.
Pete the Cat is surely one of the characters. There might also be his friends or family members who could be involved in his big lunch story.
Since we don't know the specific 'the wrong house true story', it's impossible to say who the main characters are. It could be the person who entered the wrong house, and perhaps the homeowners.
The main character is the innocent man. There may be lawyers involved in his case, both those who initially believed the false evidence against him and those who later came to his aid to prove his innocence. Also, there might be other people in the community who had an impact on the case, either by believing the false accusations or by standing up for the truth.