Shalom Kathryn. I do not disregard the fact that the term brother is also used for even just for friends. But I invite you to analyze these. Did Joseph abandon Mary when she begot Jesus? Or did was there a record in the Scriptures that Joseph did not touch Mary after Jesus was born? There is none right? So the possibility is there that Mary bore a child or children after Jesus.
Sure there's the possibility. The Scriptures are silent on the matter.
However, there is the interesting parallel between Mary and the Ark of the Covenant.
THE VIRGIN MARY AS THE ARK OF THE NEW COVENANT
"Mary, in whom the Lord himself has just made his dwelling, is the daughter of Zion in person, the Ark of the Covenant, the place where the glory of God dwells. She is 'the dwelling of God [...] with men.'" CCC#2676
God the Holy Spirit overshadowed and then indwelled the Ark. The Ark became the dwelling place of the presence of God [Exodus 40:34-35]
God the Holy Spirit overshadowed and the indwelled Mary. At that time Mary's womb became the dwelling place of the presence of God [Luke 1:35]
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The Ark contained the 10 Commandments [the words of God in stone], a pot of manna, and Aaron's rod that came back to life [Deuteronomy 10:3-5; Hebrews 9:4].
The womb of the Virgin contained Jesus: the living Word of God enfleshed, the living bread from heaven, "the Branch" (Messianic title) who would die but come back to life [Luke 1:35].
The Ark traveled to the hill country of Judah to rest in the house of Obed-edom [2 Samuel 6:1-11]
Mary traveled to the hill country of Judah (Judea) to the home of Elizabeth [Luke 1:39]
Dressed in a priestly ephod, King David approached the Ark and danced and leapt for joy [2 Samuel 6:14]
John the Baptist, son of a priest who would himself become a priest, leapt for joy in Elizabeth's womb at the approach of Mary [Luke 1:43]
David shouted for joy in the presence of God and the holy Ark [2 Samuel 6:15]
Elizabeth exclaimed with a loud cry of joy in the presence God within Mary [Luke 1:42]
David asked, "How is it that the Ark of the Lord comes to me?" [2 Samuel 6:9]
Elizabeth asks, "Why is this granted unto me, that the mother of my Lord should come to me?" [Luke 1:43]
The Ark remained in the house of Obed-edom for 3 months [2 Samuel 6:11]
Mary remained in the house of her cousin Elizabeth for 3 months [Luke 1:56].
The house of Obed-edom was blessed by the presence of the Ark [2 Samuel 6:11]
The word "blessed" is used 3 times in Luke 1:39-45 concerning Mary at Elizabeth's house.
The Ark returned to its sanctuary and eventually ends up in Jerusalem where the presence and glory of God is revealed in the newly built Temple [2 Samuel 6:12; 1 Kings 8:9-11]
Mary returned home from visiting Elizabeth and eventually comes to Jerusalem, where she presents God the Son in the Temple [Luke 1:56; 2:21-22]
God made Aaron's rod (which would be kept in the Ark) return to life and budded to prove he was the legitimate High Priest [Numbers 17:8].
God would resurrect His Son, who had become enfleshed in Mary's womb and born to bring salvation to all mankind, to prove He is the eternal High Priest [Hebrews 4:14].
In Revelation 11:19 John sees the Ark of the Covenant in heaven [this is the last verse of chapter 11]
In Revelation 12:1 John sees Mary in heaven. It is the same vision Juan Diego saw of Mary in 1531'the Woman clothed with the sun and standing on the moon.
THE VIRGIN MARY AS THE ARK OF THE NEW COVENANT
If any man touched the Ark of the Covenant, he was immediately struck dead -no human was allowed to touch the Ark. This is an argument used to bolster the doctrine of perpetual virginity.
I want to point out that the bible is also silent on whether or not Joseph was even alive during Jesus' ministry, or whether or not Jesus had biological brothers and sisters.
Just sayin'.