The Bible is not a book written by a single author, so one author can verify another.
No they can't, since it's authorship is anonymous. Also you would need to demonstrate one author was offering a credible account, anymore than another. You are making a bare appeal to numbers, it's called an argumentum ad populum fallacy.
The miracles of Jesus are verified by the writers of the gospels and the other aspects of Jesus life also.
The gospel author or authors are unknown, the names Mathew Mark Luke and John are fictitious, and were assigned centuries later, to make it appear as if they authored by disciples.
But really it is the unquestioned existence of Paul and his proximity to the life of Jesus which verifies the life and death of Jesus.
Paul never met nor knew Jesus. His claims are mostly subjective opinion after the fact, hearsay in other words.
Paul is a witness to the resurrection only in his claim to have met the risen Jesus.
So not a witness then, just claiming to have been one. If someone claims they've seen Elvis, does this make them an eyewitness to Elvis resurrection? What if they knew him personally, unlike Paul with Jesus?
Of course you believe the gospels were hearsay claims written long after the events and by anonymous authors. That is the sceptic position but it denies the evidence of history as to the authors of the gospels and denies the internal evidence in the New Testament itself concerning their dates being writing.
- information received from other people which cannot be substantiated; rumour.
The sceptic position relies on sceptic bias concerning the prophecy about the destruction of the temple and so the dates and so authorship taken as after 70AD.
This is a separate claim, and scepticism is not the same as bias, you're projecting. You however believe claims from one religion, and reject identical claims form others, so I don't bias is a word you should throw around.
This is a presumed dating system (tossing out other evidence) and is circular reasoning.