Maria Virgine

 αδελφος - brother, close relative

Here is one of many, many examples of the Greek word for brother not literally meaning brother, but rather relative:

Genesis 28:

English: New American Standard Bible

Greek OT: LXX (Septuagint)

English: King James Version

2.

"Arise, go to Paddan-aram, to the house of Bethuel your mother's father; and from there take to yourself a wife from the daughters of Laban your mother's brother.

αναστας αποδραθι εις την μεσοποταμιαν εις τον οικον βαθουηλ του πατρος της μητρος σου και λαβε σεαυτω εκειθεν γυναικα εκ των θυγατερων λαβαν του αδελφου της μητρος σου

Arise, go to Padan-aram, to the house of Bethuel thy mother's father; and take thee a wife from thence of the daughters of Laban thy mother's brother.

15.

Then Laban said to Jacob, "Because you are my relative, should you therefore serve me for nothing? Tell me, what shall your wages be?"

ειπεν δε λαβαν τω ιακωβ οτι γαρ αδελφος μου ει ου δουλευσεις μοι δωρεαν απαγγειλον μοι τις ο μισθος σου εστιν

And Laban said unto Jacob, Because thou art my brother, shouldest thou therefore serve me for nought? tell me, what shall thy wages be?

The same thing is true of the word for sister (really the same word with a feminine ending):

Genesis 24:

55.

But her brother and her mother said, "Let the girl stay with us a few days, say ten; afterward she may go."

ειπαν δε οι αδελφοι αυτης και η μητηρ μεινατω η παρθενος μεθ' ημων ημερας ωσει δεκα και μετα ταυτα απελευσεται

And her brother and her mother said, Let the damsel abide with us a few days, at the least ten; after that she shall go.

(Her mother and brother are the "they" below)

60.

They blessed Rebekah and said to her, "May you, our sister, Become thousands of ten thousands, And may your descendants possess The gate of those who hate them."

και ευλογησαν ρεβεκκαν την αδελφην αυτων και ειπαν αυτη αδελφη ημων ει γινου εις χιλιαδας μυριαδων και κληρονομησατω το σπερμα σου τας πολεις των υπεναντιων

And they blessed Rebekah, and said unto her, Thou art our sister, be thou the mother of thousands of millions, and let thy seed possess the gate of those which hate them.

John 19 - Mary's sister - Mary! Not very likely an actual sister.

25.

Therefore the soldiers did these things.But standing by the cross of Jesus were His mother, and His mother's sister, Mary the wife of Clopas, and Mary Magdalene.

ειστηκεισαν δε παρα τω σταυρω του ιησου η μητηρ αυτου και η αδελφη της μητρος αυτου μαρια η του κλωπα και μαρια η μαγδαληνη

Now there stood by the cross of Jesus his mother, and his mother's sister, Mary the wife of Cleophas, and Mary Magdalene.

(Mary of Cleophas: https://www.newadvent.org/cathen/09748b.htm)

Which is why the English below is a stumbling block to many people today, thinking that Jesus literally had brothers. But it's been a controversy way before that, too - see https://www.newadvent.org/fathers/3007.htm.

Matthew 13
55.	"Is not this the carpenter's son? Is not His mother called Mary, and His brothers, James and Joseph and Simon and Judas?	ουχ ουτος εστιν ο του τεκτονος υιος ουχι η μητηρ αυτου λεγεται μαριαμ και οι αδελφοι αυτου ιακωβος και ιωσης και σιμων και ιουδας	Is not this the carpenter's son? is not his mother called Mary? and his brethren, James, and Joses, and Simon, and Judas?

While the doctrine was not invented in the 2nd century but was apostolic in origin, this is still a pretty good article about Mary's perpetual virginity: https://en.wikipedia.org/wiki/Perpetual_virginity_of_Mary  It makes mention of how and why non-orthodox churches discarded the doctrine.

A key paragraph:

The perpetual virginity of Mary is one of the four Marian dogmas of the Catholic Church, meaning that it is held to be a truth divinely revealed, the denial of which is heresy. (The other three are her role as Theotokos (meaning mother of God), her Immaculate Conception, and her bodily Assumption into heaven). It declares her virginity before, during and after the birth of Jesus...

"Scripture Alone" (Sola Scriptura), to me, is a bad idea and contradicts orthodox Christianity. But even for the Protestants that attempt to adhere to this, as seen above, nothing in scripture proves that Mary had other children.

So why is this important?  It has to do with the authority of the Church, apostolic tradition, and divine revelation.  It has to do with God's plan and how special Mary is in that plan.  There are a lot of themes that could be developed here.  Maybe someday...