Daddy, Mama, and Brother are given only these generic names that reflect their respective positions in the family unit. They also reference all of the characters' roles in relation to Doodle. This hints that Doodle is the star of the show. Similarly, the doctor is only called "the doctor." This points out his relationship to Doodle, and might also suggest that he is just that, a generic doctor, and one who does what an average doctor would have done. Generic names might another way Brother reminds us that Doodle, who has two names, is the focus of the story. Only his names are important to Brother. Aunt Nicey is an exception. Since she is the one who really believes in Doodle from the begging, it's natural that Brother would want to us to understand, by her name, that she's nice.
But back to Doodle. Brother says that when Doodle had lived three months:
[…] Mama and Daddy […] named him William Armstrong, which was like tying a big tail on a small kite. Such a name sounds good only on a tombstone, (1.3)
On one level, Brother thinks the name sounds like the name of some old, dead relative. He sees it as another indication that his parents still think Doodle will die, as if Doodle has the burden of the "big tail" of death tied to his name. After we've read the whole story and understand that Brother believes that Doodle died because Brother expected too much from him, we see another level of meaning. Brother might even be suggesting that by giving him such a huge name, Mama and Daddy are expecting too much from him.
Both of these concerns factor into Brother's decision to rename the little guy Doodle. Brother explains that when Doodle crawls backwards, he reminds Brother of a doodle-bug. Doodle is a playful name – not a name that would look good on a tombstone. This next quote directly addresses Brother's other concern:
Renaming my brother was perhaps the kindest thing I ever did for him, because nobody expects much from someone called Doodle. (2.2)
This sounds mean until we know that Brother feels guilty for pushing Doodle beyond his physical limits. Brother is beating up on himself a little in this line. He's not saying, it was so nice of me to name my brother Doodle. He saying that naming him Doodle was the nicest thing he ever did. In other words, he thinks he didn't do enough nice things for Doodle when he was alive. We don't think this is quite fair, considering all the other nice things he did for Doodle, but we can see where he's coming from.
As we discuss in "Setting" Doodle and Brother live in a beautiful area. They both appreciate the beauty of their surroundings, and are interested in nature. Their interaction with their location gives us clues to their characters. They are happy where they live, and don't seem to want to live anywhere else. Since the scarlet ibis isn't native to North Carolina, where the boys live, location characterizes it as an outsider, or stranger, or someone who is different. Doodle too could be thought of as an outsider but it has little to do with location. Still, the ibis's location in the story links him with Doodle.