For those like me, born and bred conservative evangelical, the sanctity of the Holy Bible was unquestionable in the early years and it was reflected in the way we saw the question of human authorship of the sacred text.
Gary Cottrell has started some time ago a series of articles on his blog about the authorship of the four gospels. He writes in plain English so it should be easy on the eye and appealing for an amateur like me.
Here see few extracts, check for the whole series on his blog
The gospels are anonymous.
Tying a specific individual to each of the gospels need not become an issue of faith.
We cannot absolutely confirm or deny traditional authorship.
The author of Luke openly acknowledges that he conducted research, so we must assume that he obtained information from other sources. He also says that at least some of that information he used (either oral or written) was based on eyewitness accounts.
Most scholars believe that Mark was the first of the four canonical gospels to be written. What we find is that Matthew and Luke record parallels to Mark that are so striking that it appears possible, perhaps even likely, that both Matthew and Luke used Mark as one of the sources for their own gospels.