The historic record, both Biblical and extra-Biblical, shows that Jesus's brothers did accept him as the Christ after Jesus's death. Paul, writing in 1 Corinthians 15, reports that after his resurrection, Christ "appeared to more than 500 brothers at one time. ... Then he appeared to James, then to all the apostles." That would be Jesus's brother James -- the brother who tried to stage an intervention and would not even show up at Jesus's execution.
James became a pillar of the early church. Early church historians record that years after the resurrection, when local public officials asked James to tell others Jesus was not the Christ, James proclaimed that his brother was the Lord. The local leaders then threw James off the Temple wall in Jerusalem and stoned him to death. James and Jesus's brother Simeon then took up James' place. Their brother Jude too proclaimed Christ as the Messiah. He too was executed.
Many people reject these things as myth. The historic record shows that, regardless, the events of this week 2000 years ago fundamentally reshaped the world. More likely than not, the words "We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights" would not have happened but for Jesus first proclaiming himself "the way, and the truth, and the life."