This is a common question. People think the Greek New Testament says "brother," and translators therefore add to the Bible when they say "brother and sister." The fact of the matter is that the word "brother' is English, and the New Testament is written in Greek and says ἀδελφός. So the Bible, technically, does not say "brother." The real question is, what does ἀδελφός refer to and how do you convey the meaning in your culture?
For an Informed Love of God