Judy had read many novels and comics in this regard. A person's soul lived in another person's body and would inherit the memory of the original owner of the body.
However, the host did not necessarily inherit the memory of the original owner immediately. The host would slowly recall the memory bit by bit. Judy asked quickly and let him answer without thinking. If he was not her brother, he would definitely not be able to answer. And Judy could know whether he was her brother or not.
"You were pushed down the stone steps in your home by the nanny and got hurt when you were five years old." If Judy didn't mention it, Adam would have almost forgotten about it. Now that Judy mentioned it, he remembered the nanny who took care of her back then. That nanny actually abused a child secretly who was only a few years old.