"For Your sake I bore disgrace; humiliation covered my face. I am become a stranger to my brothers, an alien to my mother's sons; for the zeal of Your house consumed me, and the insults of those who disgraced You fell on me"
Psalm 68:8-10, Orthodox Study Bible page 726
As others have pointed out, your interpretation of this prophecy would imply that this prophecy was not fulfilled. If "mother's sons" implied that she gave birth to other children, you would have to believe that she had given birth to St. James (who is referred to as "the Lord's brother" in Galatians 1:19) and St. Jude (who refers to himself as "brother of James" in Jude 1:1). If you read the Book of Acts and the epistles of Sts. James & Jude, you would know that they were faithful followers of the Lord and did not consider him a stranger and alien.
Yet, John 19:26-27 states:
When Jesus therefore saw His mother, and the disciple whom He loved standing by, He said to His mother, "Woman, behold your son!" Then He said to the disciple, "Behold your mother!" And from that hour that disciple took her to his own home.
The Lord entrusted His mother to His disciple because He was her only Son and she had given birth to no other. Sts. James and Jude were children of St. Joseph from his former marriage. That St. Jude refers to himself as "a bondservant of Jesus Christ, and brother of James", rather than "brother of the Lord", is on account of the fact that he was the son of St. Joseph and not of the mother of the Lord, and on account of his humility. St. James also does not refer to himself as "brother of the Lord", but is referred to as such by St. Paul.
That the Psalm you quote refers to Israel is shown in many places in the New Testament, for instance John 1:11-13:
He came to His own, and His own did not receive Him. But as many as received Him, to them He gave the right to become children of God, to those who believe in His name: who were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.
"His own", meaning Israel, on the whole rejected the Lord as the Messiah. However, "as many as received him" refers to those who did believe in Him unto salvation, both of Israel and among the Gentiles. The children of Israel were "His people", "his brothers", and "his mother's sons", and they as a people did not recognize the Lord when he came. This is demonstrated by the persecutions that the Christians endured as described in the Book of Acts. However, the Book of Acts also confirms that some of Israel (a minority for sure) did accept Christ, including St. Paul and the Apostles.
St. Augustine comments on this verse from the Psalms as follows:
“An alien I have become to My brethren, and a stranger to the sons of My mother” (ver. 8 ). To the sons of the Synagogue He became a stranger…Why so? Why did they not acknowledge? Why did they call Him an alien? Why did they dare to say, we know not whence He is? “Because the zeal of Thine House hath eaten Me up:” that is, because I have persecuted in them their own iniquities, because I have not patiently borne those whom I have rebuked, because I have sought Thy glory in Thy House, because I have scourged them that in the Temple dealt unseemly:2942 in which place also there is quoted, “the zeal of Thine House hath eaten Me up.” Hence an alien, hence a Stranger; hence, we know not whence He is. They would have acknowledged whence I am, if they had acknowledged that which Thou hast commanded. For if I had found them keeping Thy commandments, the zeal of Thine House would not have eaten Me up. http://www.ccel.org/ccel/schaff/npnf108.ii.LXIX.html