Okay *cracks fingers* let's see what I do for the swap au timeline. (Elliot and Aaron are uncle and nephew in the doll and prototype swap only unless the canon says otherwise)
Doll Aaron
Elliot never adopted, but was a present uncle in Aaron's life. He took Aaron in when he lost his parents and brother and treated the boy well during the healing process. However, Aaron also later died, leaving Elliot grief-strickened by the death of his younger sister and her family, and now his nephew. So he decided to bring him back.
Poppy (or Oliver) is an adult working in the factory when an accident caused her to be knocking on death's door. Elliot took that opportunity, promising to save her if she allows him permission to do so. She agreed and got turned into a prototype, growing resentment towards Elliot for lying, keeping her trapped and uncared for after using her to bring back a dead child.
The relationship between Aaron and the prototype is a guardian and child, but sometimes they act like siblings.
Prototype Aaron
Elliot never found Oliver (or Poppy) for his experiments, gradually giving up on bringing his child back by the fruitless results he achieved. He focused his attention on his company, the public noticing a big change in Mr. Ludwig by his company growing. Then Aaron became an orphan.
He took his nephew in and gave him everything he thought the boy needed, but Aaron could see how unwanted he was. Despite being relatives, Elliot wasn't there for him, too busy with work to give attention to the grieving 12 year-old. And he did talked to him, it was always about someone else, constantly bringing her up at every chance he got. It led to an accident in the factory.
Elliot took this opportunity and "saved" Aaron from death. Nothing changed. He still talked about her, he still wasn't there for him.
The relationship between Aaron and the doll started off as a one-sided hatred, going as far as damaging the doll. But then, the BBI happened and the desire for closeness, a family, began to grow. It's more of a tyrant and subject than siblings.
