Well, Luke was one of the writers and said when writing to Theophilus:
"Many have undertaken to draw up an account of the things that have been fulfilled among us, just as they were handed down to us by those who from the first were eyewitnesses and servants of the word. With this in mind, since I myself have carefully investigated everything from the beginning, I too decided to write an orderly account for you, most excellent Theophilus, so that you may know the certainty of the things you have been taught."
Luke most likely spoke to those who were of the original disciples, since he said that he had carefully investigated everything from the beginning. Luke was the one who traveled with Paul and who wrote the book of Acts as well. Mark was the son of Mary, who was related to Barnabas and was a helper of Paul. Matthew, also called Levi, was a tax collector whom Jesus called and was one of the original disciples.
And John was also an original disciple of the Lord who wrote John and Revelation.