This phrase is basically asking the question, "How old are you in relation to your siblings" (i.e. "Are you the oldest, middle, youngest, etc. child?"). The question is asked this way because your non-dominant hand is used to index siblings and children in order of age. The phrase is signed here as: "BROTHER SISTER, YOU POINT(non-dominant index)?" with "BROTHER SISTER" signed with the topical facial expression and with "YOU POINT(non-dominant index)?" signed with the wh-word question facial expression (eyebrows down).