Well, do you have evidence that the 12 disciples did not exist? Do you have evidence that the Gospels were not written by people in a position to speak about the events?
Let's start with the Gospel of Mark. The text itself does not indicate that it was written by Mark; in fact, it was not attributed to Mark until sometime in the 2nd century.
There are also suggestions in the texts that the stories were written after
the destruction of the Temple in 70 CE. If Jesus supposedly died circa 30 CE, then the authors were probably not eye witnesses. Life expectancy was not good in that time and place -- Somewhere in the area of 40 years -- and someone who had been an adult in the supposed time of Jesus would be long dead before the destruction of the Temple.
There's also the heavy supernatural element of the stories. I'm simply not inclined to take as gospel truth (pun definitely intended) a group of stories that talk about virgin births, people coming back from the dead, and zombies roaming the streets of Jerusalem during a three-hour darkness.