Sandy and Denny Murry are depicted as typical, normal boys, who are relatively good at school and athletic. Meg mentions that Sandy and Denny do not have any problems and are never criticized or ridiculed by their peers. Sandy and Denny are popular in school and seem to conform to the rest of their class. They embody a "happy medium" and are never too rowdy or serious. Sandy and Denny seem to go through the motions and move through life without any problems. Sandy and Denny do not play a prominent role in the story and are considered flat characters.
Sandy and Denny are significantly different from the rest of their family members. Their parents are extremely intelligent, risk-taking scientists, who perform elaborate experiments at home. Their father is being held captive on the dystopian planet Camazotz while their mother is searching for various ways to reach him. Unlike the twins, Meg Murry is considered an oddball at school and struggles to get along her with teachers and peers. Meg lacks confidence and is extremely insecure. Charles Wallace is also unique and considered a child prodigy. He is significantly smarter than anyone his age and has the ability to read people's minds. Overall, Sandy and Denny are normal, typical boys, who fit in with their peers and seem to experience smooth, uneventful lives. In contrast, their family members are intelligent, unique individuals, who are exceptional in their own ways and take extreme risks.