A is VERY close to his brother. My dad and his brother are not on talking terms. I know another set who used to hang out together in the same bunch of friends, but never really seemed to talk to each other. And now that they have their own lives, I really doubt they talk to each other, not because they hate each other, but because they have nothing to talk about..
On the other hand, I don;t know any sisters who are indifferent or not on talking terms. Is this a brother thing? Not sure.