This has been covered on several other threads. Mary does indeed have other children, there are billions of us. But she only bore in her womb one, our Lord, Jesus the Christ.
PMV:
DOCTRINE: Mary’s only child was Jesus.
(Catechism #499-501)
BIBLE: Mary had other children. (Luke 8:19-21) Many Catholics argue that when the Bilbe referes to brothers of Jesus, that these are spiritual brothers and not blood relatives. Luke 8:19-21 makes a clear distinction between spiritual and blood brothers and proves that Mary did in fact have other children.
Where in the Bible does it say Mary had other children? Luke 8, 19-21 says no such thing.
Luke 8,
19 Then his mother and his brothers came to him but were unable to join him because of the crowd.
20 He was told, “Your mother and your brothers are standing outside and they wish to see you.”
21 He said to them in reply, “My mother and my brothers are those who hear the word of God and act on it.”
3 [3] Is he not the carpenter?: no other gospel calls Jesus a carpenter. Some witnesses have “the carpenter’s son,” as in Matthew 13:55. Son of Mary: contrary to Jewish custom, which calls a man the son of his father, this expression may reflect Mark’s own faith that God is the Father of Jesus (Mark 1:1, 11; 8:38; 13:32; 14:36). The brother of James . . . Simon: in Semitic usage, the terms “brother,” “sister” are applied not only to children of the same parents, but to nephews, nieces, cousins, half-brothers, and half-sisters; cf Genesis 14:16; 29:15; Lev 10:4. While one cannot suppose that the meaning of a Greek word should be sought in the first place from Semitic usage, the Septuagint often translates the Hebrew ah by the Greek word adelphos, “brother,” as in the cited passages, a fact that may argue for a similar breadth of meaning in some New Testament passages. For instance, there is no doubt that in v 17, “brother” is used of Philip, who was actually the half-brother of Herod Antipas. On the other hand, Mark may have understood the terms literally; see also Mark 3:31-32; Matthew 12:46; 13:55-56; Luke 8:19; John 7:3, 5. The question of meaning here would not have arisen but for the faith of the church in Mary’s perpetual virginity.
Read your KJV Bible, is Lot really Abram’s “brother” in Gn 14, 14? No, of course not, Lot is Abrams nephew, not his brother. The term “brother” in Scripture does not mean sibling of the same parents.