Yes they are brother and sister kodi was te last pup with aleu in the box,and kodi was adopted he becam a sled dog when he got older.And the little boy who adopted kodi is beleived to be the musher in balto 3

I am not sure if you have seen the films. If you remember in the second film Kodi and Aleu were the last two pups in the box, and in Wings Of Change if you remember Balto's flashback memory of his children as pups Aleu appears on Balto's head before Balto appears before Kodi. They were both in the same litter together. Isn't it obvious when Balto calls Aleu his "daughter" and Kodi his"son"?

Appearantly you haven't seen the films, have you? Kodi and Aleu are related. And Kodi was adopted, as seen in the very end of the adoption scene when Aleu waves goodbye to him.

Uh, yes. Also he was sold, he just apeard in balto 3.