Q: “Did Jesus have blood brothers and sisters; if so, where in the Bible does it say so?”
A: There are a number of passages in Scripture which inform us that Jesus had “brothers.” For example, in Matthew 13:55 and Mark 6:3 mention is made of James, Joses, Judas, and Simon as constituting Jesus’ brothers, and the statement is also made: “Aren’t his sisters here with us?” From the Apostle John’s account (John 7:3-5) we learn that Jesus’ own brothers did not believe in him. But it is assumed that, after his resurrection from the dead, these brothers did come to faith, and that James and Judas even became writers of the New Testament letters bearing their names (see Jude 1, James 1:1, Gal. 1:19, and I Cor. 15:7).
Do the words “brothers and sisters” mean offspring of Mary and Joseph (half-brothers and half-sisters of Christ), or is it simply cousins that are being referred to here in these verses? It is true that sometimes the word “brother” can simply mean “cousin”; the Greek word for “brother” has a number of different uses. The Eastern Orthodox Church regarded Jesus’ “brothers” as indicating children of Joseph by a former wife. Due to the influence of the Roman Catholic Church in wanting to maintain Mary as “semper virgine” (always a virgin, even after the conception and birth of Christ), many theologians, including Luther, opted for the meaning “cousins.” Of course, the reason why Rome feels compelled to preserve Mary as “semper virgine” is to maintain, what they say, is her status as “all holy and free from every stain of sin.” Apparently it was felt that if Mary would have had normal sexual relations with sinful Joseph after Jesus’ birth, this would destroy their doctrine of Mariolatry.
We Protestants, of course, have no problem with assuming that Mary and Joseph had natural husband and wife relations after Christ’s birth. According to the Scriptural admonition in I Cor. 7:5, we would find it hard to believe that there was any such sexual abstinence. The natural explanation, and the most logical, is to take the expression “brothers and sisters” to mean the blood half-brothers and half-sisters of our Lord.