my favourite theory on the other JC is that Jesus and Jesus Barabas could have been the same person.
Taking this from a starting point of assuming that there is no magic version of Jesus - but that he's an actual historical Jewish figure who was co-opted into being a deity after his death. I understand that some may fundamentally disagree with that, but please humour me.
So Barabbas means "son of the father" - and isn't it just a bit too much of a coincidece that 2 men named Jesus also know as the son of the father were crucified on the same day.
Also as good as jesus' message sounds even today, it seems unlikely that the whole "be excellent to each other" vibe is enough alone to gather much of a following - certainly not enough to flourish into a major world religion.
Some accounts state that Jesus Barabbas was a leader of a Jewish rebellion against Roman occupation - throughout history this is the kind of figure that is far more likely to gather a large following and hero worship than some do-gooder.
Think about all the people throughout history that have had a date system based on them - they've mostly been military leaders, or leaders of great empires.
Could it be possible that Jesus was a charismatic leader of a Jewish rebellion against Roman occupation and corruption in the Jewish elite - he was caught and executed but his followers thought fomr some reason that he would return to help end the occupation.
Many years later he still has a following, so his life story is rewritten to become more divine and less guerilla fighter, in order to be more fitting as the head of the religion it was becoming.
Could have happened that way.
alternatively the story of Jesus Barabas could have been made up entirely as a contrast to Jesus christ