I have found many analyses. Do you know of any one that focuses on Sonny's brother and his life, in James Baldwin's short story "Sonny's Blues?"
In "Sonny's Blues" by James Baldwin, the narrator is Sonny's unnamed brother.
The narrator is older, and he promised his mother before she died that he would take care of Sonny. When he insisted that Sonny would be all right, being a good boy, she tells her older son:
"It ain't a question of his being a good boy," Mama said, "nor of his having good sense. It ain't only the bad ones, nor yet the dumb ones that gets sucked under."
The narrator, it turns out, is in better shape to care for Sonny than Sonny himself first because the brother has a job as a teacher of high school math—and Sonny falls prey to drugs. As the story begins, Sonny and his brother have lost touch. The narrator discovers that Sonny was arrested for dealing and using heroin; the narrator becomes scared for Sonny—he feels as if there is ice water running through his veins. This shows that though there is distance between them, the narrator still cares about his brother.
After his arrest, Sonny is put in jail; it takes a long time before the narrator finally contacts Sonny. Sonny's letter speaks of how much he needs his brother. The narrator feels guilty, and makes sure to stay connected...from then on, he writes to Sonny all the time. When Sonny is released, the narrator meets his brother when he returns to New York.
One thing that prevents the narrator from understanding Sonny has been his willingness to "kill himself" by using drugs. While there is a gap of seven years in their ages, the narrator hopes this age difference might unite them in some way. His tie to Sonny is still strong:
I was remembering, and it made it hard to catch my breath, that I had been there when he was born; and I had heard the first words he had ever spoken. When he started to walk, he walked from our mother straight to me. I caught him just before he fell when he took the first steps he ever took in this world.
In this passage, the reader hears not only the narrator's memories of a young brother, but memories that a parent would treasure of his or her child. This shows that the narrator has accepted the role his mother placed upon him years before of his brother's guardian.
The narrator does not understand Sonny's "blues." He expects that if Sonny is going to pursue music, it would be classical, but Sonny loves jazz. When he plays it, it comes from his soul. It is not until the narrator hears his brother play that he catches a glimpse of the stranger that is his younger sibling—a man the narrator has never known:
Creole started into something else...it was Am I Blue. And, as though he commanded, Sonny began to play...they all came together again, and Sonny was part of the family again...Then they all gathered around Sonny and Sonny played...Sonny's fingers filled the air with life, his life...it was no longer a lament...we could cease lamenting.
The narrator sees his brother's gift for music—how the music speaks for his brother, and how his brother speaks through the music.
The last line of the story mentions a drink brought to Sonny's piano, and alludes to Isaiah 51:22. Baldwin writes:
...it glowed and shook above my brother's head like the very cup of trembling.
The Bible verse speaks of the end of God's anger (the "cup of trembling"), and a promise to the end of His fury...
...thou shalt no more drink it again.
We sense a relief in the narrator, a deeper understanding of Sonny, and hope for his brother's future.