Idk, I definitely call both my brothers bro, but I'm also 10 yrs younger than one and 21 yrs older than the other. They're also both half-bros tho, so maybe that's it
I've also used brochacho here and there since learning it
my siblings and I call each other then most derogatory nicknames we for each other since we used to argue and fight a lot growing up unless shit is serious. then it's "hey (actual name)"
my home life wasn't super stable so I wonder how many families have this kind of sibling relationship