Ariel has six older sisters in Disney's The Little Mermaid.
They are Attina, Alana, Adella, Aquata, Arista, and Andrina. Together with Ariel, they are the seven daughters of King Triton in the 1989 animated film. The sisters appear near the beginning during the performance of “Daughters of Triton,” where their names are introduced in song before Ariel is discovered to be missing.
Ariel is the youngest of the seven sisters, which is why the answer is six rather than seven. The family detail is easy to miss because the sisters have only a brief role in the original film, while Ariel's relationship with Triton and her friendship with Flounder and Sebastian receive most of the story's attention.
The six sisters also appear in Disney's 2023 live-action remake, although that version gives them different names: Perla, Indira, Mala, Caspia, Tamika, and Karina. That change can create confusion when viewers compare the two films, but both versions preserve the basic family structure: Ariel is Triton's youngest daughter with six older sisters.