I’m not quite as concerned with getting absolute proof that they were Jesus’ brothers. It seeems we need absolute proof that Mary had no children. Even if there was no mention of children, that wouldn’t prove she was otherwise childless, or a perpetual virgin.
Given that Joseph was her husband, and they lived as husband and wife for at least the 33 years up to Jesus’ death, I think someone needs to provide proof in the form of a positive statement from the Bible or historical records that Joseph was a virgin. Because the bible clearly indicates that husbands and wives are supposed to sleep together, and the bible doesn’t say Joseph had a concubine, another wife, or was an adulterer, so if Mary was a virgin, then Joseph was as well.
And THAT is so impossible to believe that you need proof for it — much more so than any incredulity about younger siblings giving counsel to an older sibling.
Heck, we aren’t even told that Joseph was given some special dispensation such that he could live his life without ever having sex.
The Bible doesn't say that. Joseph is not mentioned after the episode where they find Jesus in the Temple at the age of 12 years.
Because the bible clearly indicates that husbands and wives are supposed to sleep together
Well, no, not always. In fact, priests serving the Temple were prohibited from contact with their wives during the period of their service.
Think about the implications for someone who lived in daily proximity to God-in-the-flesh.
As was pointed out, we don’t know anything (biblically) about Joseph after Jesus was 12. After re-reading that scripture, it doesn’t even mention Joseph by name, just ‘his parents’. I don’t know what tradition says, but Mary could have been remarried. Perhaps a guy named ‘Cleophas’, maybe had some kids with him.