Welcome to Catholic Answers Forum! I will be happy to address the verses you listed… But before we can really do that, we have to step back a bit to get the big picture first.
When Catholics call Mary the “Blessed Virgin,” they mean she remained a virgin throughout her life. When Protestants refer to Mary as “virgin,” they mean she was a virgin only until Jesus’ birth. They believe that she and Joseph later had children whom Scripture refers to as “the brethren of the Lord.” The disagreement arises over biblical verses that use the terms “brethren,” “brother,” and “sister.”
There are about ten instances in the New Testament where “brothers” and “sisters” of the Lord are mentioned (Matt. 12:46; Matt. 13:55; Mark 3:31–34; Mark 6:3; Luke 8:19–20; John 2:12, 7:3, 5, 10; Acts 1:14; 1 Cor. 9:5).
When trying to understand these verses, note that the term “brother” (Greek: adelphos) has a wide meaning in the Bible. It is not restricted to the literal meaning of a full brother or half-brother. The same goes for “sister” (adelphe) and the plural form “brothers” (adelphoi). The Old Testament shows that “brother” had a wide semantic range of meaning and could refer to any male relative from whom you are not descended (male relatives from whom you are descended are known as “fathers”) and who are not descended from you (your male descendants, regardless of the number of generations removed, are your “sons”), as well as kinsmen such as cousins, those who are members of the family by marriage or by law rather than by blood, and even friends or mere political allies (2 Sam. 1:26; Amos 1:9).
Lot, for example, is called Abraham’s “brother” (Gen. 14:14), even though, being the son of Haran, Abraham’s brother (Gen. 11:26–28), he was actually Abraham’s nephew. Similarly, Jacob is called the “brother” of his uncle Laban (Gen. 29:15). Kish and Eleazar were the sons of Mahli. Kish had sons of his own, but Eleazar had no sons, only daughters, who married their “brethren,” the sons of Kish. These “brethren” were really their cousins (1 Chr. 23:21–22).
The terms “brothers,” “brother,” and “sister” did not refer only to close relatives. Sometimes they meant kinsmen (Deut. 23:7; Neh. 5:7; Jer. 34:9), as in the reference to the forty-two “brethren” of King Azariah (2 Kgs. 10:13–14).
No Word for Cousin
Because neither Hebrew nor Aramaic (the language spoken by Christ and his disciples) had a special word meaning “cousin,” speakers of those languages could use either the word for “brother” or a circumlocution, such as “the son of my uncle.” But circumlocutions are clumsy, so the Jews often used “brother.”
The writers of the New Testament were brought up using the Aramaic equivalent of “brothers” to mean both cousins and sons of the same father—plus other relatives and even non-relatives. When they wrote in Greek, they did the same thing the translators of the Septuagint did. (The Septuagint was the Greek version of the Hebrew Bible; it was translated by Hellenistic Jews a century or two before Christ’s birth and was the version of the Bible from which most of the Old Testament quotations found in the New Testament are taken.)
In the Septuagint the Hebrew word that includes both brothers and cousins was translated as adelphos, which in Greek usually has the narrow meaning that the English “brother” has. Unlike Hebrew or Aramaic, Greek has a separate word for cousin, anepsios, but the translators of the Septuagint used adelphos, even for true cousins.
You might say they transliterated instead of translated, importing the Jewish idiom into the Greek Bible. They took an exact equivalent of the Hebrew word for “brother” and did not use adelphos in one place (for sons of the same parents), and anepsios in another (for cousins). This same usage was employed by the writers of the New Testament and passed into English translations of the Bible. To determine what “brethren” or “brother” or “sister” means in any one verse, we have to look at the context. When we do that, we see that insuperable problems arise if we assume that Mary had children other than Jesus.
When the angel Gabriel appeared to Mary and told her that she would conceive a son, she asked, “How can this be since I have no relations with a man?” (Luke 1:34). From the Church’s earliest days, as the Fathers interpreted this Bible passage, Mary’s question was taken to mean that she had made a vow of lifelong virginity, even in marriage. (This was not common, but neither was it unheard of.) If she had not taken such a vow, the question would make no sense.
Mary knew how babies are made (otherwise she wouldn’t have asked the question she did). If she had anticipated having children in the normal way and did not intend to maintain a vow of virginity, she would hardly have to ask “how” she was to have a child, since conceiving a child in the “normal” way would be expected by a newlywed wife. Her question makes sense only if there was an apparent (but not a real) conflict between keeping a vow of virginity and acceding to the angel’s request. A careful look at the New Testament shows that Mary kept her vow of virginity and never had any children other than Jesus.