Conjecture is not Scripture. It's only the same kind of reasonings that leave one spiritually afloat and lost without the compass that points truly to Jesus and security forever.
Don't waste your time on this kind of thing.
Mary did have more children, and at least some of them were influential in the days when the literature of the New Covenant was being written. The Book of James, her son, half-brother to Jesus, was one of the earliest letters sent to the churches, warning them of imposters.
The same kind of imposters are mightily active today, and need sharp, decisive reproof.
No, Mary didn't have more children. James was the son of Joseph by a previous marriage.
Epiphanius the bishop of Salamis wrote in 'The Panarion' (AD 374-375) that "... James (brother of Jesus) was Joseph's son by Joseph's first wife, not by Mary".
Clarification:
What part exactly does Paul say is a sin?
Love,
O2