I have not yet read much of the article you provided a link to, but it quotes a well known passage in one of the writings of Josephus which says "... the brother of Jesus, who was called Christ, whose name was James ...". [By the way that passage is one of the key historical sources which caused me to be convinced enough in the Bible and thus get baptized while a teenager. I learned of that passage in the WT's 1969 book called Is the Bible really the Word of God? on page 63 of the book, when I was trying to determine if the Bible was true. The same book includes the quote of Tacitus about one called Christus whom Tacitus says the extreme penalty by procurator Pontius Pilate. That was also a key reason for me becoming sure that Jesus did exist as a historical person, and thus a major part of the reason while I got baptized as a JW before age 16.]
Regarding the passage of "... the brother of Jesus, who was called Christ, whose name was James ..." the web page which you linked to also says the following.
"Modern scholarship has almost universally acknowledged the
authenticity of the reference to "the brother of Jesus, who was called
Christ, whose name was James" (τὸν ἀδελφὸν Ἰησοῦ τοῦ λεγομένου Χριστοῦ,
Ἰάκωβος ὄνομα αὐτῷ) and has rejected its being the result of later Christian interpolation.[37][38][39][40]
Moreover, in comparison with Hegesippus' account of James' death, most
scholars consider Josephus' to be the more historically reliable.[35] Some scholars have noted Josephus is more sympathetic to James than his brother.[41] '
The same web page also says 'Paul mentions meeting James "the Lord's brother" (τὸν ἀδελφὸν τοῦ
κυρίου) and later calls him one of the pillars (στύλοι) in the Epistle to the Galatians[46] Galatians 1:18-2:10: ... But I saw none of the other apostles except James the Lord's brother. (In what I am writing to you, before God, I do not lie!)'
While I was an active baptized JW (at least during most of that time if not during the earliest part of that time when I was a teenager and thus knew less of the Bible) I believed that Jesus had fleshly brothers and sisters (contrary to what the Catholic Church teaches, but in agreement to what the WT teaches). That is because the gospels of mark and Matthew says he had such, and that one of his brothers was named James. During all of the subsequent time periods when I still definitely believed that Jesus was a historical person I continued to believe that Jesus had a brother named James. Perhaps none of the brothers of Jesus was the one known as James the Great or James the Just, but I see no reason to believe that fleshly non-supernatural historical Jesus had a brother (even if only a half-brother) named James. During the period of time when I believed in the Christ myth concept (such as described by Earl J. Doherty in his book called The Jesus Puzzle: Did Christianity Begin with a Mythical Christ?) about Jesus and thus didn't believe that a historical Jesus existed, I thus didn't believe Jesus had a brother named James, but after doing more research and contemplation I stopped believing in the Christ myth concept about a year or so ago.
Please consider the Wikipedia article called
Brothers of Jesus which says the following.
' Mark 6:3 names James, Joses, Judas (conventionally known in English as Jude) and Simon as the brothers of Jesus, and Matthew 13:55, which probably used Mark as its source, gives the same names in different order, James, Joseph, Simon and Judas.[8]
"Joseph" is simply the longer form of "Joses", and so it appears that
James was the eldest and Joses/Joseph the next, but as Matthew has
reversed the order of the last two it is uncertain who was the youngest.[9] Unnamed sisters are mentioned in Mark 6:3 and Matthew 13:56 and may be implied in Mark 3:35 and Matthew 12:46, but their number is unknown.[3]
The gospels indicate a rift between Jesus and his brothers in the early part of his ministry (see Mark 3:31-35 and the parallel passages in Matthew 12:46-50 and Luke 8:19-21), and they never appear among his followers during his lifetime.[10] John has Jesus's brothers advising him to go to Judea
despite being aware that his life would be in danger, and they are
absent from his burial, which should have been their responsibility,[11] but they do appear in Acts 1:14
with the Eleven (i.e., the remaining disciples after the betrayal by
Judas Iscariot): "These all (the Eleven) were persevering in prayer
along with the women, with Mary the mother of Jesus, and with his
brothers."[11]
In 1 Corinthians 15:3–7 Paul lists a "James" among those to whom the risen Christ had appeared,[12] and most scholars agree that this refers to James the brother of Jesus.[13] The 2nd century historian Hegesippus (c.110 – 180 AD) reports that James the brother of Jesus came to be known as James the Just,[14] and Eusebius of Caesarea (died 339) says that he spent so much of his life in prayer that his knees became "like the knees of a camel."[15] According to Clement of Alexandria, reported by Eusebius, he was chosen as bishop of Jerusalem,[16] and from the time when Peter left Jerusalem after Herod's attempt to kill him (Acts 12) he appears as the principal authority in the Jerusalem church, presiding at the Council of Jerusalem recorded in Acts 15.[16] In Galatians 1:19
Paul tells how he went to Jerusalem a few years after his conversion
and met Cephas (Peter) but no other apostles, only "James, the brother
of the Lord";[17] Paul's Greek leaves it unclear whether he includes, or does not include, James among the apostles.[18] '
Since Josephus mentions John the Baptist/Baptizer, and says even more about him than about Jesus, I also believe that John the Baptist/Baptizer had existed. Even when I believed that Jesus never existed I still believed John the Baptist/Baptizer had existed.