Perhaps his best friend. This friend could be the one who was with him right before the accident and blames himself for not stopping Peter from getting too close to the tracks. He would then be a key character in the story, trying to make amends in some way while also being there for Peter's family.
Maybe it's his sister, Mary. Mary could have some idea about why Peter has locked himself away. She might be torn between respecting his privacy and wanting to help him. She could be bringing him food and leaving little notes outside his locked door, trying to communicate with him.
Ned could be another main character. He could come over to Peter's place to keep him company while he's in pain. They could end up playing video games or Ned could be trying to cheer Peter up by showing him some new Star Wars collectibles he got.
Definitely Aunt May. She would be super worried about baby Peter and would do everything she could to take care of him. She might even call in some old friends or neighbors to help out.
In 'peter is hit by a train fanfiction', it could be a very dark and dramatic story. The train hitting Peter could be the start of a journey into the afterlife. He might meet strange entities or have to face his own inner demons. His physical body could be in a critical state in the real world while his spirit is on this otherworldly adventure.
Tony Stark could be another important character. He has been a sort of mentor to Peter in the original stories. In this fanfic, he might be a bit jealous at first that Bucky has this new role in Peter's life. But eventually, he could also contribute to Peter's growth, perhaps by providing new technology for Peter's Spider - Man suit in light of Bucky's more hands - on combat training.
Mary Jane could be a great addition. She could be the one who helps Peter deal with the emotional turmoil of having Venom as part of him. Another good character is Ned. He could be the tech - support, trying to find ways to control or enhance Venom's powers. And of course, there's Doctor Octopus. He could be a great villain in the fanfiction, either trying to steal Venom's powers or team up with it against Peter.
Lois could be a great addition. Her relationship with Peter and her reactions to his antics with Quagmire can add a lot of drama. Also, Cleveland. His calm and collected nature contrasts with Peter and Quagmire's craziness. His interactions with them can lead to some really funny moments.
Mary Jane could be a great character to include. Her strong personality and acting aspirations could bring a different flavor to the story. Norman Osborn could also be in the story. As the head of Oscorp, he could be the mastermind behind some of the problems that Ava and Peter face, or he could be a more ambiguous figure, sometimes helping and sometimes causing trouble.
His best friend could be a main character. This friend might be the one who rushes to Peter's side when he starts bleeding and tries to comfort him.
There could also be new characters created specifically for the fanfiction. Maybe a new love interest for one of the Peters, or a sidekick that is unique to this particular fan - made story. This new character could bring a fresh dynamic to the relationship between the two Peters.