Here's a link to a good brief summary on Wikipedia
Brother is the lead protagonist of the story and also the narrator. He is not given a name but is referred to by Doodle, his brother, only as "Brother." He is six years old when Doodle is born. Brother has a high opinion of his own ability to run, jump, and climb, and wants a brother with whom he can share these activities. When it becomes clear that Doodle is capable of little more than lying on a rubber sheet and crawling backwards, Brother grows ashamed of Doodle's limitations and regularly taunts him. Though Brother loves Doodle, the love is tainted with cruelty and embarrassment.
Doodle is the mentally and physically retarded younger brother of the narrator, Brother. His family initially calls him by his given name, William Armstrong, but Brother nicknames him Doodle. Doodle's real strengths lie not on the level of his physical prowess, but on a more subtle inward level, to which Brother seems blind at the time the action takes place. From the beginning of his life, Doodle defies death and refuses to recognize the coffin that Daddy builds for him as his own. He shows a sense of wonder and respect for the natural world, crying with wonder at the wild beauty of Old Woman Swamp.
The other characters are Daddy, Mama and Aunt Nicey.
"The Scarlet Ibis" is the story of two brothers, one, the narrator, called Brother, and the younger of the two, Doodle. Doodle is born a very sickly child, whom no one expects to live, and whom Brother feels a tremendous amount of, for lack of a better word, shame. Brother wanted someone who could run and jump and play with him; instead he got the fragile Doodle. Determined to make him into the brother that he wants, Brother pushes him constantly past the point of physical endurance; he is often cruel to him, even making him touch the coffin that was originally built for him as a baby. Doodle does learn a lot from Brother, but everything he learns comes at a very high and dangerous price to Doodle in the end.
"The Scarlet Ibis" is a story about two brothers. The narrator is the big brother and little brother is Doodle. The narrator was so ashamed to have a brother like that, he even decides to kill the baby by smothering him with a pillow. He stop and sees Doodle smile and realizes that he is smart. The narrator is sometimes mean to Doodle. He showed Doodle the coffin threatening him to leave him there. Doodle begs his brother to never abandon him. The Brother was embarrassed that Doodle still couldn't walk so he sets out to teach him. On Doodle's 6th birthday, doodle surprises the family by walking. Brother decides to teach him to be athletic like him. Doddle shows signs of weaknesses. They find a scarlet ibis in their yard. Doodle is sad and he buries it. Later on the brother makes Doodle row the boat. Doodle is exhausted. A storm approaches and doodle and his brother run home. The brother runs ahead of him and when his anger calm, he runs back to find Doodle curled up. Doodle was bleeding from his mouth. The scarlet Ibis symbolizes him. The Brother is cruel, his pride took over him.