Red: Werewolf Hunter

The modern-day descendant of Little Red Riding Hood, Virgina, brings her fiancé, Nathan, home to meet her family. Virgina's brother Marcus and Jake are quick to welcome Virgina back, affectionately calling her "Red". Jake explains its a family nickname passed down to the first daughter every generation.After Nathan finds a man staggering up the driveway half dead. The dying man says the name "Gabriel" before Nathan runs for Virginia. When they return, the man is already ashes. The sheriff arrives and contains the situation, much to Nathan's dismay. Virgina takes Nathan inside and explains that they hunt werewolves. Nathan, not believing her, goes for a walk at sunset. He is attacked and bitten by a werewolf who reveals his name to be Gabriel.The next day, while preparing for a hunt, Nathan asks if they had ever turns a werewolf back. Virgina tells him that the only way to break the curse is to kill the wolf who turned the person, before they kill a human on their first full moon.Shortly after, they go hunting in town where Nathan succeeds in killing a werewolf while the rest of the group attacks a few others. After the wolves are dead, they find a girl locked in their trunk. She tells them that the wolves are planning on a "Game" that no human comes out of.Later that night, while setting up camp, Nathan transforms into a wolf for the first time. Desperate to protect him, Virgina insists on locking him up for the night. Nathan awakes the next morning in a cell. With the curse over, for the night he is released for the day, to help hunt Gabriel.Back in town, Marcus and Jake are taken captive for the new "Game". When the night comes to an end, its revealed that the brothers were killed during the night.The next day the family prepare for a final battle, and Gabriel seizes the moment to kidnap Virgina. Nathan finds the brothers shortly before finding Virgina. The couple return home and finish preparations for the full moon. As the sun goes down, the battle begins. Nathan is locked in his cage with the Grandmother watching him. Red kills several of the werewolves who enter the house, before confronting Gabriel.Meanwhile, the grandmother tries to shoot Nathan as he turns into a werewolf. Upon escaping from the cell, Nathan, in werewolf form, kills the grandmother.Upstairs, Virgina is pursued by Gabriel. Smearing her blood stained hand in silver paint, she smears it on Gabriel, who falls over the rail, two stories. Virgina jumps after him, plunging a silver headed harpoon into his heart. As he dies, Virgina hears the howl of a werewolf. Fearing the worst, she flees to the basement to see Nathan, but finds her Grandmother dead. Grabbing a red cloak, Virgina runs to the woods to find Nathan. Werewolf Nathan attacks Virgina, knocking her out.In the morning, Virgina discovers she's been bitten. Several feet from where she fell was a trail of blood leading to an old ruined building. Inside, Nathan is human again. He pledges his love to Virgina, saying he wants a life with her. As he hugs her, Virgina stabs him with a silver knife, swearing she'll always love him.The movie ends with Virginia reading the story of Little Red Riding Hood to a little girl as a wolf howls in the distance.

Question: Who is in charge of watching Nathan in the cell?
Answer: grandmother