Who, how many are the authors of the book of Genesis? How credible are its authors?

The rest of the Bible is mostly a book of History many events of which can be checked out with other sources, while the doctrinal parts are often the work of a well defined prophet/saint, but, how credible are the authors of Genesis? Could it be just a collection of ideas and beliefs with little or no authority at all?
Traditionally, Genesis was finished mostly by Moses, having the creation stories and stories of Abraham handed down to him (and the Hebrews) by previous generations. 

I think rather than asking about the credibility of Genesis, one should question the credibility of the Torah (1st 5 books of the OT). While narrative books such as Chronicles and prophetic books like Isaiah are shown OVER TIME by the Jews to be inspired, the Torah has been considered by the Jews as sacred and inspired for many generations - at least from 9th century (depending on what date you want to give the Torah). 

It's historical credibility boils down to how one believes the world was created and whether the flood actually happened etc. Some are convinced that there is scientific evidence to back creation as well as the flood. It really depends on what you're willing to be open to - whether you want to look into evidence for creation and the flood.
Other than that, Genesis' credibility can be found in its theology. It's the theology and philosophical truths of Genesis that has made the Jews believe in its divine inspiration and, therefore, has given the author credibility.