The Twins were two of the forty applicants in Season 4. They were portrayed by twin sisters Melinda Dahl (Twin #1) and Caitlin Dahl (Twin #2) and were assigned numbers 15A and 15B respectively. Their names were never revealed in the series.
The Twins had a frequent habit in The Right Stuff of arguing with each other over each other's respective diagnoses. Gregory House, who admitted to fantasizing about them, often admonished them about how distracting their arguments were.
Although they survived until the final ten, they were both blamed for Thirteen's failure to ensure the patient in 97 Seconds took the ivermectin for his Strongyloides. They were both dismissed at that point.