Why the disciple took Jesus' mother unto his own home? 26 When Jesus therefore saw his mother, and the disciple standing by, whom he loved, he saith unto his mother, Woman, behold thy son!
27 Then saith he to the disciple, Behold thy mother! And from that hour that disciple took her unto his own home. - KJV John 19:26,27

We are not seeing Joseph near cross? Why did Jesus hand over his mother to his disciple? Where are his brothers and his father? Is there a history attached to it?
SO, according to Tradition, Joseph had long since passed when Jesus even began his ministry, making him ineligible. The next question is "Why didn't Jesus entrust his mother to one of his step-brothers then?" 


There is no substantial evidence that he had step-brothers. As the Aramaic word for "brother" is better understood "kinsman", it is quite possible that Christ had no step-brother, only kinsmen (meaning that he may have only had cousins)
The Apostle John WAS A COUSIN of Christ. The point is made here, but if you really want a better explanation you should contact Dr. Glasov at Seton Hall University. He has a cool chart and some nifty textual criticism.
As both a cousin and the beloved disciple, John was in the unique situation of being both the most faithful to Christ and a close blood relative. As such, he was probably the best choice to be given this honor.