It could also imply that 'my brother who doesn't' isn't Benedict, therefore he would be the second brother.Funny. I got that right.
It says: Benedict, my brother who doesn't.... - implying you have a brother who does.
Not: Benedict, my brother, who doesn't.... - which says Benedict is your brother.
Read it through logically and it's clear there's a sister who lives in Madrid, a brother who doesn't, and another brother who's whereabouts (or lack thereof) isn't even mentioned.I'd like to introduce you to my sister Clara, who lives in Madrid, to Benedict, my brother who doesn't, and to my only other sibling, Hilary.