King Triton has seven daughters, with Ariel as the youngest.
In Disney’s The Little Mermaid continuity, Triton’s daughters are Ariel, Attina, Alana, Adella, Aquata, Arista, and Andrina. The six older sisters appear with Ariel in the opening “Daughters of Triton” sequence, introducing the royal family before Ariel’s fascination with the human world becomes the story’s central conflict.
Ariel’s position as the seventh daughter helps explain why she is treated as both the youngest child and a particularly protected member of the family. The sisters also reinforce the film’s oceanic royal setting and are commonly associated with the seven seas.
The number can be confused with Hans Christian Andersen’s original fairy tale, which has a different family arrangement. It is also easy to count only Triton’s older daughters and answer six; however, the question asks for all of his daughters, including Ariel.