Yes, he could be. If the story focuses on the family's Christmas experience from a child's perspective, the kid brother might be the main character. His reactions to the Christmas traditions, like decorating the tree or waiting for Santa, can drive the story forward.
In A Christmas Story, the kid brother is often a source of both chaos and charm. He's part of the family dynamic, adding to the humorous and sometimes hectic situations in the family during the Christmas season.
I don't know the name of the brother. It could be a detail that's easy to miss. Maybe you could look up a summary or discussion about the story to find out.