The text tells us that all of the dead at the cemetery make their voices heard in the decision to keep or banish Bod.
According to Neil Gaiman, "death is the great democracy." This means that all humans must eventually die, no matter who they are. In that sense, all humans are considered equal in the face of death. So, in terms of deciding whether to keep Bod at the graveyard, none of the dead can claim precedence in terms of wisdom or position. In the story, all the inhabitants of the graveyard are dead and so, must have equal voice in the decision.
Of course, the decision is not an easy one. Josiah Worthington rightly argues that the graveyard is no place for a living, human baby. Yet, because of the danger Bod is in, the inhabitants of the graveyard must do everything they can to protect the child. In the end, three hundred voices are raised in reference to the matter. Each one of the dead clamors to be heard; yet a conclusive decision is not reached until the Lady on the Grey appears on her horse. Her words, "The dead should have charity" decides the course of action the graveyard inhabitants will take.
This is how Bod comes to spend his formative years at the graveyard. Mr. and Mrs. Owen volunteer to be Bod's parents, while Silas offers to be Bod's guardian. Between them and the rest of the dead, they do an admirable job in preparing Bod to meet his nemesis in battle.