“Is not this the carpenter’s son? Is not his mother called Mary, and his brethren James, and Joseph, and Simon, and Jude: And his sisters, are they not all with us? Whence therefore hath he all these things?” (Mt. 13: 55-56)
“Is not this the carpenter, the son of Mary, the brother of James, and Joseph, and Jude, and Simon?
Are not also his sisters here with us?” (Mk. 6:3)
“For neither did his brethren believe in him” (Jn. 7:2-9)
“But other of the apostles I saw none, saving James the brother of the Lord” (Ga. 1:19)
At times, the term “brethren” refers to Jesus’s disciples in general, or His “cousins”, the sons of Joseph’s brother, Alphaeus (or Clopas/Cleophas): Simon, Joseph, Judas (Thaddeus), and James (James the Less/Just) – the latter two apostles. And, the reason James of Alphaeus was referred to as “brother of the Lord” was because He resembled Jesus in manner and demeanor.
Additionally, Alphaeus, and his two sons, Simon and Joseph, did not believe in what Jesus was preaching and doing, and it made them angry. Alphaeus remained angry and hateful up until his death bed, though Simon and Joseph eventually came to believe and become disciples.
Furthermore, in regards to “His sisters”, it refers to the women disciples. To name a few:
Mary of Joseph (Jesus’s mother)
Mary of Alphaeus (or of Clopas/Cleophas)
Mary Salome (wife of Zebedee)
Mary of Clopas (daughter-in-law to Mary Salome)
Mary of Bethany or Mary Magdalene (sister to Lazarus of Bethany)
Martha of Bethany (sister to Lazarus of Bethany)
Joanna of Chuza (Chuza was house-steward of Herod Antipas)
Annaleah of Jerusalem
Eliza of Bethzur
Marcella
Nike
Porphirea
Susanna
Sarah
…and so on