Marla Kate Sorenson (née Larsen) is the mother of Seth and Kendra Sorensen. Her parents are Grandma and Grandpa Larsen and her husband is Scott Sorenson. Ruth and Stan Sorenson tried to hint at magical creatures but she never let on.
By the end of the fourth book, it is revealed that, unfortunately, Scott and Marla were kidnapped by the Society of the Evening Star.
At the end of the fifth book, they are rescued from Living Mirage. By then they are aware of the magical world, and they are informed of Kendra and Seth's heroics.