There are plenty of other supporting verses to contend that Mary did indeed have other children.
Matthew 1:18-25 Now the birth of Jesus Christ took place in this way. When his mother Mary had been betrothed to Joseph, before they came together she was found to be with child from the Holy Spirit. And her husband Joseph, being a just man and unwilling to put her to shame, resolved to divorce her quietly.
But as he considered these things, behold, an angel of the Lord appeared to him in a dream, saying, “Joseph, son of David, do not fear to take Mary as your wife, for that which is conceived in her is from the Holy Spirit. She will bear a son, and you shall call his name Jesus, for he will save his people from their sins.” All this took place to fulfill what the Lord had spoken by the prophet: “Behold, the virgin shall conceive and bear a son, and they shall call his name Immanuel” (which means, God with us). When Joseph woke from sleep, he did as the angel of the Lord commanded him: he took his wife, but knew her not until she had given birth to a son. And he called his name Jesus.
Psalm 69:8 I have become a stranger to my brothers, an alien to my mother's sons.
Matthew 1:24-25 When Joseph woke from sleep, he did as the angel of the Lord commanded him: he took his wife, but knew her not until she had given birth to a son. And he called his name Jesus.
Matthew 12:46-47 While He was still speaking to the multitudes, behold, His mother and brothers were standing outside, seeking to speak to Him. And someone said to Him, “Behold, Your mother and Your brothers are standing outside seeking to speak to You.”
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?”
Mark 6:2-3 And when the Sabbath had come, He began to teach in the synagogue; and the many listeners were astonished, saying, “Where did this man get these things, and what is this wisdom given to Him, and such miracles as these performed by His hands?”... “Is not this the carpenter, the son of Mary, and brother of James, and Joses, and Judas, and Simon? Are not His sisters here with us?”
Luke 2:6-8 And while they were there, the time came for her to give birth. And she gave birth to her firstborn son and wrapped him in swaddling cloths and laid him in a manger, because there was no place for them in the inn.
John 2:12 After this He went down to Capernaum, He and His mother, and His brothers, and His disciples; and there they stayed a few days.”
Acts 1:14 These all with one mind were continually devoting themselves to prayer, along with the women, and Mary the mother of Jesus, and with His brothers.
1 Corinthians 9:4-5 Do we not have a right to eat and drink? Do we not have a right to take along a believing wife, even as the rest of the apostles, and the brothers of the Lord, and Cephas?
Galatians 1:19 But I did not see any other of the apostles except James, the Lord’s brother
Strong's Concordance
http://biblehub.com/greek/80.htm
adelphos: a brother
Original Word: ἀδελφός, οῦ, ὁ
Part of Speech: Noun, Masculine
Transliteration: adelphos
Phonetic Spelling: (ad-el-fos')
Short Definition: a brother
Definition: a brother, member of the same religious community, especially a fellow-Christian.
Here is a link to the occurrences of the Greek word *adelphos*.
http://biblehub.com/greek/80.htm
The word *sister* (adelphe) in the Greek is the same.
http://biblehub.com/greek/79.htm
The word used is *brother* not *cousin*.
It can't mean a member of the same religious community in the context in which they occur, because then that would mean every man in Israel could be identified as Jesus' brother. So that would not identify Jesus as anyone in particular's brother.
It's not going to mean *brother in Christ* as that concept was not yet in place and the Jews, who knew Jesus as a Jew and knew His brothers as Jews, would not even begin to understand the new birth and what being in Christ meant.
They didn't even understand who JESUS was, much less being a *brother in Christ*.
The only definition left then, is to mean physical brother.
And it would not be *cousin*.
The word for *relative* that is used for Elizabeth is *suggenes*, not *adelphe*.
http://biblehub.com/greek/4773.htm
Strong's Concordance
suggenes: akin, a relative
Original Word: συγγενής, ές
Part of Speech: Adjective
Transliteration: suggenes
Phonetic Spelling: (soong-ghen-ace')
Short Definition: akin, a relative
Definition: akin to, related; subst: fellow countryman, kinsman.
Joseph and Mary had sex just like any other normal couple and just like almost every other couple, they had a bunch of kids. His brothers are named and He had at least three sisters.
And from a cultural standpoint, three incidents support Catholic and especially the Orthodox tradition.
1. Jesus told John to care for his mother. Why should he do this if he had three brothers?
2. Jesus’ brothers tried to boss him around. No, with Joseph dead, the oldest brother becomes head of the family, and younger brothers would not do such a thing. Again, this hints they were older brothers.
3. When Jesus went missing at age 12, both Mary and Joseph went to look for him. But if there were younger siblings, why did Mary take them on such a dangerous journey to Jerusalem in the first place, let alone go tramping around Jerusalem with a baby or toddler who needed supervision and or breast feeding?
Finally, outside of western Europe, extended families are the norm. The reformers projected their own cultural bias into their interpretations which you quote,
79. ἀδελφή adĕlphē, ad-el-fay´; fem. of 80; a sister (nat. or eccles.):—sister.
80. ἀδελφός adĕlphŏs, ad-el-fos´; from 1 (as a connective particle) and δελφύς dĕlphus (the womb); a brother (lit. or fig.) near or remote [much like 1]:—brother.
81. ἀδελφότης adĕlphŏtēs, ad-el-fot´-ace; from 80; brotherhood (prop. the feeling of brotherliness), i.e. the (Christian) fraternity:—brethren, brotherhood.
[STRONG, J., A Concise Dictionary of the Words in the Greek Testament and The Hebrew Bible 1, 8.]
Here's another source on Adelphos:
81 ἀδελφός (adelphos), οῦ (ou), ὁ (ho): n.masc.; ≡ DBLHebr 278; Str 80; TDNT 1.144—1. LN 10.49 brother, male sibling (Mt 4:18); 2. LN 11.23 fellow believer, a male and/or female, believer in the believing community (Ro 8:29); 3. LN 11.25 fellow Jew (Ac 22:1); 4. LN 11.57 fellow countryman (Ac 2:29), see also prior; 5. LN 11.89 neighbor(Mt 5:22) note: these entries may overlap in verses and entries...
[SWANSON, J., Dictionary of Biblical Languages with Semantic Domains: Greek (New Testament),.]
It can be cousins, but the term is clearly broadly applied.I don't think its necessarily cousins in all instances. It might be simply "neighbor" or simply "kinsmen" but if we understand adelphos as simply cousin in every passage that also makes sense because Hebrew has no word specifically for "cousin." Adelphos is clearly a broadly used word for kinsmen and cousins and not one narrowed to blood brothers only.
Thus that is the best reading of your references: (Matthew 12:46-47) (Matthew 13:55)(Mark 6:2-3)(Luke 2:6-8)(John 2:12)(Acts 1:14)(1 Corinthians 9:4-5)(Galatians 1:19)
[Notation from Ignatius Catholic Study Bible]
Matt 12:46 his brethren: The NT often mentions Jesus’ brethren (13:55; Mk 3:31; 6:3; Lk 8:19; Jn 2:12; 7:3; Acts 1:14; Gal 1:19). The Church maintains, however, that Jesus’ Mother, Mary, remained a virgin throughout her life. These so-called brethren of Jesus are thus his relatives but not children of Mary. Four observations support the Church’s tradition: (1) These brethren are never called the children of Mary, although Jesus himself is (Jn 2:1; 19:25; Acts 1:14). (2) Two names mentioned, James and Joseph, are sons of a different “Mary” in Mt 27:56 (Mk 15:40). (3) It is unlikely that Jesus would entrust his Mother to the Apostle John at his Crucifixion if she had other natural sons to care for her (Jn 19:26–27). (4) The word “brethren” (Gk. adelphoi) has a broader meaning than blood brothers. Since ancient Hebrew had no word for “cousin”, it was customary to use “brethren” in the Bible for relationships other than blood brothers. In the Greek OT, a “brother” can be a nearly related cousin (1 Chron 23:21–22), a more remote kinsman (Deut 23:7; 2 Kings 10:13–14), an uncle or a nephew (Gen 13:8), or the relation between men bound by covenant (2 Sam 1:26; cf. 1 Sam 18:3). Continuing this OT tradition, the NT often uses “brother” or “brethren” in this wider sense. Paul uses it as a synonym for his Israelite kinsmen in Rom 9:3. It also denotes biologically unrelated Christians in the New Covenant family of God (Rom 8:29; 12:1; Col 1:2; Heb 2:11; Jas 1:2)
[MITCH, C., “Introduction to the Gospels”, The Ignatius Catholic Study Bible: The New Testament (San Francisco 2010) 29-30.] Its a fairly flimsy argument you made, because no where in extent sources of later letters by Christian writers were people asserting that Mary had other sons. Not one of your passages claims them to be the sons of Mary just to reecho my prior source. The Bible doesn't reference other "sons or Mary or Joseph" anywhere. So clearly Jesus had no siblings.