I think the idea behind the question is to find out how much responsibility u have in your family, to help them assess how easily u can detach yourself from family and face work. They want to know if ur responsibilities at home will affect your ability to give ur best at work. They probably are also interested in finding out your kind of relationship you have with your siblings. And if that is correct, then u flopped big time by 4getting their ages. In my case, they wanted to know my position in the family and what all my siblings do for a living. However, even tho' every question in an interview is important since they target different assessments, I still think this should be one of the not-so-important issues.