Commenting on the claim forwarded by Jerome and most modern Catholic apologists that the term αδελφος can mean a near-relative (e.g., a cousin), and not just a uterine sibling, Margaret Wesley noted one glaring problem with this view:
Linguistic defense of this view relies on the lack of a word for cousin in Hebrew. The Hebrew, ah, is usually translated into Greek as αδελφος when it may have originally meant cousin. Meier notes Oberlinner’s discovery that only one such translation can be found (1 Chron 23:22) and further point out that because of the ambiguity of ah the narrator usually clarifies the nature of the relationship, as in 1 Chron 23:22. Clearly, no such clarification is given in the Gospel writers’ use of the word αδελφος in relation to Jesus’ brothers.
It is also hard to see why Jerome’s concerns about “translation Greek” would be relevant to the Gospels, which were all, with the possible exception of Matthew, written in Greek. There is certainly no reason to think that Paul is translating from the Hebrew when he uses τον αδελφον του κυριου to describe James in Gal 1:19 where τον ανεψιος του κυριου would have been more accurate had James been merely a cousin of Jesus. (Margaret Wesley, Son of Mary: The Family of Jesus and the Community of Faith in the Fourth Gospel [Australian College of Theology Monograph Series; Eugene, Oreg.: Wipf and Stock, 2015], 36-7)
Indeed, after surveying the various theories of the brothers and sisters of Jesus (pp. 36-42), Wesley clearly comes down on the Helvidian perspective (i.e., the brothers and sisters were children of both Mary and Joseph, the functional position of Latter-day Saints):
Absolute proof is certainly not available, but the balance of probability is heavily weighted in the direction of Jesus’ brothers and sisters being the offspring of both Mary and Joseph. I am sufficiently satisfied to allow this to form an assumption for the remainder of this book. (Ibid., 42)
For more on the perpetual virginity of Mary, including a discussion of the meaning of αδελφος in the New Testament, see chapter 4 of my book Behold The Mother of My Lord: Towards a Mormon Mariology entitled "The Perpetual Virginity of Mary" (pp. 83-138).