it depends, this may be survivorship bias, because when a brother is a villain, it is usually the eldest
however, when a brother isn't the villain, the protagonist is usually the firstborn. especially in the Fairy Books, there's a bunch of mentions of "so-and-so had other 19 younger brothers and sisters" and things like that
War and Peace really struck a chord with me, especially Pierre and Andrei. Something about how they go through what would be a full character arc in another book, and then... keep living, and growing, and changing. Pierre tries a bunch of stuff in finding happiness in life, some of it sticks, some doesn't, but the way both of them keep persevering got me really hard.
But it's not though. As I said in another comment, it's like when movie directors keep releasing director's cuts and ruining their own movie, or when comicbook artists retcon stories from way before with new coloring that looks like ass because "new audiences wouldn't like the old stuff".
For an author to try and grab the stuff they published, which is now out there and which people have read, and to try and rework that and change the whole of the prose, it's a shitty cash grab that more often than not takes the old stuff from circulation.
It's like when George Lucas did the whole special effects things in the original Star Wars trilogy and took the original versions from circulation, as if he was the sole arbiter of all things Star Wars and not like his work of art had entered pop culture - and, therefore, isn't just his to keep tinkering.
Also I don't think the author gets to do that. That story isn't theirs to do as they please, it's been put out there, it belongs to everyone who's read it.
yeah, I usually think of books the same way as someone telling me a story
like, if my mom goes "and then I went to the bank and saw Judy there" I don't picture the bank and Judy, I just kinda acknowledge the existence of both in my head, idk how to explain it