Who is Fishtail, Ten Snow from The Birchbark House and what is their importance?

Fishtail and Ten Snow are friends of Omakayas' family. Fishtail is described as a powerful warrior, and Ten Snow as a patient, talented, and beautiful woman. The couple is extremely close and enjoy a happy marriage. This fact is evidenced when Fishtail attempts suicide after Ten Snow's death from smallpox.