Indeed, I believe most of the disciples (except Matthew, I think) were illiterate. I don't believe he's generally held to be the author of The Gospel of Matthew, though.

However, this doesn't preclude the idea of their evangelism being recorded by someone else.

Paul—while not an Apostle himself—is generally held to be the true author of at least some of his letters and is likely the closest we'll find to identifying the earliest authors of the new testament with real, historical figures.