A: We know that Mary never had any kids after Jesus because she was a virgin her whole life as many documents show, including the Bible. When the Bible talks about Jesus' brothers it is speaking about his brothers in the Holy Spirit, as in the apostles and other disciples. You may have heard the common saying among Christians, “You are my brother (or sister) in Christ.” This is the same thing. We are all members of God's family and are all brothers and sisters whether blood related or not.
Another possibility is that when translated the Aramaic word means cousins. So in the Bible when it mentions Jesus' brothers it could also mean cousins.
Karen
"And the Lord said to me: This gate shall be shut, it shall not be opened, and no man shall pass through it: because the Lord the God of Israel hath entered in by it, and it shall be shut."
-- Ezekiel 44:2.