I have had to edit your question down to just one question according to enotes regulations. The climax to this memorable tale comes significantly after the family discovers the dead scarlet ibis in their yard which impacts Doodle so greatly. It is key to realise how Hurst uses this incident to foreshadow what is about to happen. After Doodle has buried the ibis, he and his brother go to continue their training to prepare Doodle for school. As the narrator and Doodle have to cope with their awareness of failure in preparing Doodle physically to be like the other boys, Doodle waits for a consoling word from his brother, but as the storm breaks, the narrator, overwhelmed by his own shame and sense of spite, runs away, leaving Doodle:
He had failed and we both knew it, so we started back home, racing the storm. We never spoke (what are the words that can solder cracked pride?), but I knew he was watching me, watching for a sign of mercy. The lightning was near now, and from fear he walked so close behind me he kept stepping on my heels. The fast i walked, the faster he walked, so I began to run.... When the deafening peal of thunder had died, and in the moment before the rain arrived, I heard Doodle, who had fallen behind, cry out, "Brother, Brother, don't leave me! Don't leave me!"
In spite of this plea, the narrator's "streak of cruelty" is awakened through his failure to train Doodle, and so he runs away. It is this break in their fraternal relationship that is the climax of the story, because the narrator has to also face his own pride and guilt in wanting to make Doodle something he is not. After this, the narrator returns down the path to find his "scarlet ibis" dead, huddled under a bush.