I am guessing here, but I say your brother, who has experience with venomous reptiles { you claim } overreacted like an idiot when that tiny little thing struck at him, he broke her neck and won't admit it, and you are too ashamed to admit you know he did it.
If he "inspects" your snakes before purchase like you claim, there is no way on God's green earth he did not see that. A blind person could find that. He hurt her by being an idiot, and he doesn't want to admit it. So he hides behind his bluff and bluster "he's too experienced to have done that" and worse, you are letting him do it.
You both need to grow up, admit what happened, do the right thing by this baby who will never recover, and do some serious thinking before you rush out and buy another. If someone who handles venomous snakes was scared of a flea bite from that tiny little baby, maybe he should seriously consider NOT handling venomous snakes. That is just pathetic.
Gale