Sorry, Marie-Hélène but I need to correct your correction. "Do you have a brother or sister?" is a well formed question - there's nothing wrong with it. The alternative, which I think you are suggesting, would be "Do you have any brothers or sisters?" My response to either of these is yes, I have two brothers.

what is the point of this question?

Hi I have two brothers.

hi, I stand being the eldest now since my brother passed away, and I got two younger sisters. :)

yes dear..but why you asking this?