The Fall of the House of Usher: Who is behind the deaths of Roderick Usher's children?

In the Netflix miniseries, "The Fall of the House of Usher," the central mystery revolves around the deaths of all the children of Roderick Usher, the CEO of Fortunato Pharmaceuticals. In the first episode, titled "A Midnight Dreary," it is revealed that Roderick's children have died under mysterious circumstances. However, Roderick believes that their deaths are connected and blames himself for their fate. He also claims to have seen a woman wearing a plague doctor mask at three of his children's funerals, and he believes she is involved in their deaths.The series is structured around three stories that Roderick tells to Assistant US Attorney Auguste Dupin. The first story explains the connection between Roderick and his sister Madeline to Fortunato Pharmaceuticals. It is revealed that their mother used to work for the pharmaceutical owner, Mr. Longfellow, and that Roderick and Madeline are actually his children. When their mother falls ill, Roderick and Madeline ask for Mr. Longfellow's help, but he refuses. Their mother dies at home, and they bury her in their backyard. However, her body mysteriously leaves the grave and kills Mr. Longfellow.In the second story, Roderick explains what happens to the Usher family after they are targeted by an informant with information about their questionable business practices. The family begins to suspect each other, and Roderick and Madeline introduce a non-disclosure agreement to try and weed out the informant. They also offer a bounty for the capture of the traitor. Despite their efforts, they are unable to identify the informant.The third story revolves around a New Year's Night years ago when Roderick and Madeline met a bartender named Verna. This encounter is said to be a turning point in their lives, but the details are not revealed. Roderick sees Verna again after receiving shocking news from his personal physician, and he believes she may be connected to the deaths of his children.The first episode ends on