“Mark the cousin [a·ne·psi·os′] of Barnabas.” (Ac 23:16; Col 4:10) In Luke 21:16, the Greek words syg·ge·non′ (relatives, such as cousins) and a·del·phon′ (brothers) both occur, showing that the terms are not used loosely or indiscriminately in the Greek Scriptures.  

Matthew 1:25; notice the word until, indicates Mary did not remain a virgin her whole life. 

Some haved to tried to argue their way out of that truth. Thought the gospels several times point fact. However scholars have noted two things about the theories, that Mary borne no other children: One there is a motivate behind such theories, to uphold a doctrine that arouse much later; the church teaching that Mary remained a virigin throught her life. Two, the theories themselves do not hold up to under scrutiny for example, one such theory suggests that the brothers in question were step brothers, sons of Joseph by a earlier marriage. This notion lacks substance for it would it would actually deny Jesus the legal right of inherit the kingship of David, another theory is, that were actually cousins of Jesus although the Greek scriptures use distinct words for brother, cousin, and relative. Thus scholar Frank E. Gableline calls these theological theories far fetched he concludes the most natural way to understand brother is that term refers to sons of Mary and Joseph they were brothers of Jesus on his mother’s side.

Matt. 13:53-56, Jerusalem Bible: “When Jesus had finished these parables he left the district; and, coming to his home town, he taught the people in their synagogue in such a way that they were astonished and said, ‘Where did the man get this wisdom and these miraculous powers? This is the carpenter’s son, surely? Is not his mother the woman called Mary, and his brothers [Greek, a•del•phoi´] James and Joseph and Simon and Jude? His sisters [Greek, a•del•phai´], too, are they not all here with us?’” (On the basis of this text, would you conclude that Jesus was Mary’s only child or that she had other sons as well as daughters?)

The New Catholic Encyclopedia (1967, Vol. IX, p. 337) admits regarding the Greek words a•del•phoi´ and a•del•phai´, used at Matthew 13:55, 56, that these “have the meaning of full blood brother and sister in the Greek-speaking world of the Evangelist’s time and would naturally be taken by his Greek reader in this sense. Toward the end of the 4th century (c. 380) Helvidius in a work now lost pressed this fact in order to attribute to Mary other children besides Jesus so as to make her a model for mothers of larger families. St. Jerome, motivated by the Church’s traditional faith in Mary’s perpetual virginity, wrote a tract against Helvidius (A.D. 383) in which he developed an explanation . . . that is still in vogue among Catholic scholars.”
Mark 3:31-35, JB: “His mother and brothers now arrived and, standing outside, sent in a message asking for him. A crowd was sitting round him at the time the message was passed to him, ‘Your mother and brothers and sisters are outside asking for you’. He replied, ‘Who are my mother and my brothers?’ And looking round at those sitting in a circle about him, he said, ‘Here are my mother and my brothers. Anyone who does the will of God, that person is my brother and sister and mother.’” (Here a clear distinction is drawn between Jesus’ natural brothers and his spiritual brothers, his disciples. No one claims that the reference to Jesus’ mother means anything different from what it says. Is it consistent, then, to reason that his natural brothers were not that but were perhaps cousins? When what is meant is not brothers but relatives, a different Greek word [syg•ge•non´] is used, as at Luke 21:16.)