Not "always". In a large family, when the outsider would not know or would not care who exactly is a biological brother, adopted brother, half-brother, step-brother, cousin, the generic term is "brother". The examples of that are Lot and Abram eing "brothers". In the New Testament we see the same usage: in Mark 6:3 Jesus is called brother of James, and Joseph, and Jude, and Simon, but in Mark 15:40 it is another Mary who is named as the mother of the fisrt two.
This does not prove that Jesus had no biological siblings -- the scripture does not contain such proof -- but it proves that the teaching that Mary the Mother of God remained virgin, which the Church held based on the historical knowledge outside the scripture -- does not contradict the scripture.
They could have come right out and said, "And after Mary had given birth, she and Joseph lead a celibate life as husband and wife, remaining ever virgin, having no other children but Jesus"; and called those who Catholics say were cousins, "cousins" instead of "brothers" and "sisters".
Then Matthew 13:55-56 could have read....
Is not this the carpenter's son? is not his mother called Mary? and his brethren cousins, James, and Joses, and Simon, and Judas? And his sisters cousins, are they not all with us? Whence then hath this man all these things?
Or in Matthew 12:46-48 While he was still speaking to the people, behold, his mother and his brothers cousins stood outside, asking to speak to him. But he replied to the man who told him, "Who is my mother, and who are my brothers cousins ?"
But then, Jesus' response in verses 49 and 50 would have made no sense. Matthew 49-50 And stretching out his hand toward his disciples, he said, "Here are my mother and my brothers! For whoever does the will of my Father in heaven is my brother and sister and mother."
Or why wasn't it written as: And stretching out his hand toward his disciples, he said, "Here are my mother and my brothers cousins! For whoever does the will of my Father in heaven is my brother cousin and sister cousin and mother."
The Greek words used here are "adelphoi" and "adelphai", which in Greek are clearly "brother" and "sister".
The Greek word for "cousin" (Colossians 4:10) is "anepsios", which means "cousin" or "sister's son". Totally different words.
Which brings us back to the question of why it's so important that Mary have remained a virgin her entire life and Jesus had no siblings?
Why make a doctrine and teach it as fact about something at is so poorly substantiated, indeed even has Scripture stating contrary to it?
In the New Testament we see the same usage: in Mark 6:3 Jesus is called brother of James, and Joseph, and Jude, and Simon, but in Mark 15:40 it is another Mary who is named as the mother of the fisrt two.
OK, then you do conceed that the Mary listed in Mark 15:40 is the mother of more sons than just Jesus. Because the next argument is that Mary had a blood sister named Mary.
Quite frankly I am tired of hits topic so I am going to play the Ace up the sleeve card.
Matthew 1:24-25 "Then Joseph, being aroused from sleep, did as the angel of the Lord commanded him and took to him his wife, and did not know her till ('έως') she had brought forth her firstborn Son. And he called His name Jesus. "
Joseph "knew" his wife. So much for the virginity.
The "firstborn", 'πρωτότοκον' part is a bit more sketchy since it is found in the Textus Receptus, rather than Tischendorf's or Wescott-Hort. But rest assured, Rome did manage to leave 'primogenitum' in the Vulgate, and thus you need to accept the idea that Joseph and Mary had other sons after her first.