[boatbums]

John the Baptist, Christ’s cousin, was at the Cross with the Blessed Mother. Where were all these siblings? And why did Christ entrust His Mother to His cousin and not a sibling?

You mean the John the Baptist that got beheaded by King Herod shortly after Jesus began His ministry? The "John" who was the ONLY Apostle brave enough to be there at the cross was the John who wrote the Gospel Of John, the epistles of John and Revelation. If even the Apostles were so cowardly to hide while the Lord was being crucified, what makes anyone think Jesus' brothers (who didn't even believe in who He was) would show up? Jesus gave His mother's care to John because he was there.

[TBP]

Those books are probably pseudepigraphic, like most of the others.