Okay, so I was browsing certain scriptures, and I came across this.

Mark 6:3
Is not this the carpenter, the son of Mary, the brother of James, and Joseph, and Jude, and Simon? are not also his sisters here with us? And they were scandalized in regard of him.

This is the quote that protty suggest that Jesus had immediate brothers and Mary, the mother of Jesus, had them. But if you'll look at this here...

   

Mark 16:1
And when the sabbath was past, Mary Magdalen, and Mary the mother of James, and Salome, bought sweet spices, that coming, they might anoint Jesus.

And then this here...

   

Matthew 27:56
Among whom was Mary Magdalen, and Mary the mother of James and Joseph, and the mother of the sons of Zebedee.


Salome was the wife of Zebedee. The mother of James and Joseph was another Mary, because obviously if they were talking about the mother of Jesus, Jesus would have been mentioned as one of this Mary's offspring.

If I recall, it's known from Tradition that James, Simon, and Jude were blood brothers to one another, all 3 the sons of Cleophas.  And I believe that Cleophas was either the brother or half-brother of St. Joseph.

While there's a lot of modernistic-sounding drivel in many CE articles, this part works:

http://www.newadvent.org/cathen/02767a.htm

The decisive proof, however, is that the father and mother of at least two of these "brethren" are known to us. James and Joseph, or Joses, are, as we have seen, the sons of Alpheus, or Clopas, and of Mary, the sister of Mary the Mother of Jesus, and all agree that if these are not brothers of the Saviour, the others are not. This last argument disposes also of the theory that the "brethren" of the Lord were the sons of St. Joseph by a former marriage. They are then neither the brothers nor the step-brothers of the Lord. James, Joseph, and Jude are undoubtedly His cousins. If Simon is the same as the Symeon of Hegesippus, he also is a cousin, since this writer expressly states that he was the son of Clopas the uncle of the Lord, and the latter's cousin. But whether they were cousins on their father's or mother's side, whether cousins by blood or merely by marriage, cannot be determined with certainty. Mary of Clopas is indeed called the "sister" of the Blessed Virgin (John 19:25), but it is uncertain whether "sister" here means a true sister or a sister-in-law. Hegesippus calls Clopas the brother of St. Joseph. This would favour the view that Mary of Clopas was only the sister-in-law of the Blessed Virgin, unless it be true, as stated in the manuscripts of the Peshi..ta version, that Joseph and Clopas married sisters. The relationship of the other "brethren" may have been more distant than that of the above named four.

For the record, I don't believe that Our Lady had any sisters.  I believe the story that Clopas was the brother of St. Joseph as related by Hegesippus.