There are several verses in the bible that contradict the belief that Mary did not have any children besides Jesus and therefore, remained a virgin.
Some of the verses are:
Mat 1:24-25 - "And Joseph arose from his sleep, and did as the angel of the Lord commanded him, and took as his wife, and kept her a virgin until she gave birth to a Son; and he called His name Jesus."
Mat 12:46-47 "While He was still speaking to the multitudes, behold, His mother and brothers were standing outside, seeking to speak to Him. And someone said to Him, "Behold, Your mother and Yourbrothers are standing outside seeking to speak to You."
Mat 13:55- "Is not this the carpenters son? Is not His mother called Mary, and His brothers, James and Joseph and Simon and Judas?"
Mark 6:2-3 - "And when the Sabbath had come, He began to teach in the synagogue; and the many listeners were astonished, saying, "Where did this man get these things, and what is this wisdom given to Him, and such miracles as these performed by His hands? "Is not this the carpenter, the son of Mary, and brother of James, and Joses, and Judas, and Simon? Are not His sisters here with us?"
John 2:12 - "After this He went down to Capernaum, He and His mother, and His brothers, and His disciples; and there they stayed a few days."
Acts 1-14- "These all with one mind were continually devoting themselves to prayer, along with the women, and Mary the mother of Jesus, and with His brothers."
1 Cor 9:4-5 - "Do we not have a right to eat and drink? Do we not have a right to take along a believing wife, even as the rest of the apostles, and the brothers of the Lord, and Cephas?"
Gal 1:19- "But I did not see any other of the apostles except James, the Lords brother."
The contention of the Catholic church is the greek word "adelphos" for brother or "adelphe" for sister can also be used to refer to "cousins". The problem with this argument is that the context of the passages will also change and not make sense. For example in Mat 13:55, carpenter is literaly understood as Joseph, and mother is literaly understood as Mary, so the use of "cousins" switches contextual meanings in the middle of a sentence.
In order to fully understand the use of the greek words in question, you have to also look at Psalm 69 which is clearly a messianic psalm. Jesus quotes Psalm 69:4 in John 15:25 and Psalm 69:9 in John 2:16-17. Psalm 69-4-9 reads:
"Those who hate me without a cause are more than the hairs of my head; Those who would destroy me are powerful, being wrongfully my enemies, What I did not steal, I then have to restore. 5O God, it is Thou who dost know my folly, And my wrongs are not hidden from Thee. 6May those who wait for Thee not be ashamed through me, O Lord God of hosts; May those who seek Thee not be dishonored through me, O God of Israel, 7Because for Thy sake I have borne reproach; Dishonor has covered my face. 8I have become estranged from my brothers, and an alien to my mothers sons. 9For zeal for Thy house has consumed me, And the reproaches of those who reproach Thee have fallen on me."
This messianic psalm clearly shows that Jesus had brothers. The answer is inescapable. Biblically Mary had other children which biblically invalidates the belief that Mary remained a virgin.