Yes, James, the half brother of Jesus, the natural son of Mary and Joseph, was the leader of the Jerusalem church, not Peter. Don't forget Jude, another half brother of Jesus, who wrote the book of Jude. I wonder what the names of the half sisters of Jesus were? We just don't know. I hope all the half brothers and half sisters of Jesus became true Christians, like James and Jude did. We just don't know for sure. 😇
We know Jews highly valued genealogy, and made a point of recording it (So and so begat...). We also know the only person “born of Mary” (Matthew 1:18) was Jesus. We also know that John the Baptist was the son of Elizabeth “she bore a son” (Luke 1:57).
No place else in Scripture does it say Mary bore other children, nor does it say other children were “born of” Mary.
Additionally, should Jesus had siblings born of Mary, would they not have likely had children and so on? However, we don’t see that, either in the Bible, or other accounts. The Bible appears to indicate the line of both Joseph and Mary stop at Jesus (and John the Baptist, respectively). If it didn’t, when did it? Where were they at Pentecost, the crucifixion, or other key moments in His ministry?
It is my personal opinion there were no other children or half-siblings. I also believe the Apostles had no children, though we know Peter was/had been married.