According to Bart Ehrman,there is no indication within these texts that they were written by eye witnesses. According to Ahmed Deedat, these COULD NOT have been written by the apostles because they are written in the 3rd person and not the first.

Let us first deal with Bart Ehrman's objection:
In John 21;24, after we read the event of Christ telling Peter to follow him, we come to something quite interesting. Within this section, the author writes concerning himself and informs the readers that he was THIS DISCIPLE whom Jesus loved. He says that he testifies to these things and that he WROTE THEM DOWN. As we know, the disciple whom Jesus loved was an eyewitness and even walked with Jesus during his earthly ministry.

Still objections arise towards such a passage. Because of the words WE and HIS,(We know that his testimony is true.
) many come to think that this could not have been written by the apostle, despite it saying that IT WAS, just before this sentence is read. The problem is, if John did not add this little piece to his work, many would still object saying that his testimony is not true because there is no one else who can testify that what he says is true. This concept is also found within John 8 and in Matthew 18. So the reason why John included this WE is because he did not want the readers believing that this was just a story which he fashioned out of his own mind. It is very likely that other eye witnesses were present at the time this passage or this gospel was written in order to testify that what John wrote was true  

Now onto Ahmad Deedats argument:
The first point I want to make is that the gospels are not meant to be a biography of the author, but a biography of Jesus. Hence, we can understand why they used the third person in their writings. The second point to note is that when we look at John’s gospel, he never refers to himself as ME or I, but as John and the disciple whom Jesus loved. These are in the 3rd person. Yet, in John 21:25 he changes from speaking in the 3rd person to speaking in the 1st. This displays unto us the way in which the apostles wrote, mainly, that they wrote in the third person using their OWN NAMES and words like HIM when speaking about themselves, despite it being THEM who authored the texts.