maybe someone can answer this question, lets say if mark, matthew, luke and john did indeed wrote the gospels as the early church fathers say why are the gospels so dependent on each other and copy each other?
Two (Matthew and John) were eyewitnesses to the events. Mark scribed what Peter, another eyewitness, saw with his own eyes. Luke deliberately and assiduously collected accounts from eyewitnesses to write a proper historical account.
Why would we NOT expect some dependencies?
At the same time, because they are the accounts of different eyewitnesses we can expect some discrepancies.
I am not sure why this is a problem.
It isn’t clear that they, strictly speaking, “copied” each other. There are similarities in parts of the Gospels and that has been explained as a function of common sources. Mark, no doubt, talked to Luke and possibly Matthew and John. This was a relatively small community in the first century and paths would have crossed.
A good resource is
Jesus and the Eyewitnesses by Richard Bauckham. So are the writings and online materials from people like Brant Pitre (Who Was Jesus?), NT Wright, Gary Habermas, Peter J. Williams and Daniel Wallace, among others. J Warner Wallace has done some solid, but accessible, work, as well.
Try this one as a starting point:
youtu.be/r5Ylt1pBMm8