...use of the term first born strongly implies a second born and possibly more
Even an only child is called a firstborn, so how does Jesus having been called "firstborn" "strongly imply" He had siblings?
Nowhere is a near relative like uncle, cousin, nephew etc. used for adelphos
Incorrect. See below.
אָח ('âch; plural 'âchiem)
Definition
Strong
A primitive word; a
brother (used in the widest sense of literal relationship and metaphorical affinity or resemblance (like
H1)): - another, brother (-ly), kindred, like, other. Compare also the proper names beginning with «Ah-» or «Ahi-».
Greek Equivalent Words:
Strong #:
80 ‑ ἀδελφός (ad‑el‑fos')...
ἀδελφός (adelphos; plural adelphoi)
Definitions
Liddell-Scott-Jones
2. kinsman, ib.Ge.13.8, al.;...
The Septuagint translators substituted the Hebrew words "
אחים" ('âchiem) in Gen. 13:8 with the Greek equivalent "
ἀδελφοὶ" (adelphoi) and "
אָח" ('âch) in Gen 14:14 with the Greek equivalent "
ἀδελφός" (adelphos) to show
kinship between Abraham and Lot, which lineage shows were that of
uncle and
nephew: "εἶπεν δὲ Αβραμ τῷ Λωτ Μὴ ἔστω μάχη ἀνὰ μέσον ἐμοῦ καὶ σοῦ καὶ ἀνὰ μέσον τῶν ποιμένων μου καὶ ἀνὰ μέσον τῶν ποιμένων σου. ὅτι ἄνθρωποι
ἀδελφοὶ ἡμεῖς ἐσμεν." (Gen. 13:8) and "ἀκούσας δὲ Αβραμ ὅτι ᾐχμαλώτευται Λωτ ὁ
ἀδελφὸς αὐτοῦ, ἠρίθμησεν τοὺς ἰδίους οἰκογενεῖς αὐτοῦ, τριακοσίους δέκα καὶ ὀκτώ, καὶ κατεδίωξεν ὀπίσω αὐτῶν ἕως Δαν." (Gen. 14:14)
The Septuagint translators substituted the Hebrew word "
אָח" ('âch) in Gen. 29:15 with the Greek equivalent "
ἀδελφός" (adelphos) to show
kinship between Jacob and Laban, which lineage shows were that of
uncle and
nephew: "Εἶπε δὲ Λάβαν τῷ ᾿Ιακώβ· ὅτι γὰρ
ἀδελφός μου εἶ, οὐ δουλεύσεις μοι δωρεάν· ἀπάγγειλόν μοι, τίς ὁ μισθός σου ἐστί;" (Gen. 29:15
The Septuagint translators substituted the Hebrew word "
אחים" ('âchiem) in 1 Chr. 23:21–22 with the Greek equivalent "
ἀδελφοὶ" (adelphoi) to show it was
kin the daughters of Eleazar married, which lineage shows was their
cousins: "καὶ ἀπέθανεν Ελεαζαρ, καὶ οὐκ ἦσαν αὐτῷ υἱοὶ ἀλλ᾽ ἢ θυγατέρες, καὶ ἔλαβον αὐτὰς υἱοὶ Κις
ἀδελφοὶ αὐτῶν." (1 Chr. 23:22)
As you can see, one of the definitions of the word "
ἀδελφός" (adelphos) is "kinsman," and it can be used to refer to a sibling, cousin, nephew, uncle, etc. In Matt. 13:55/Mk. 6:3, Joseph, Simon, James, and Judas (Jude/Thaddeus) are called Jesus's "brothers," or "ἀδελφός" (adelphos). The context in this verse shows they were His kinsmen. However, information needed to determine the
type of kinship, e.g., sibling, cousin, nephew, uncle, etc., between Jesus and His kinsmen is lacking in those same verses and others.
I've provided evidence that
confirms Joseph, Simon, James, and Judas (Jude/Thaddeus) in Matt. 13:55/Mk. 6:3 were Jesus's brothers, as in kinsmen, and
shows that the
type of kinship between them and Jesus was that of cousins, not siblings as you believe. This was accomplished primarily by identifying James. See opening post.