The story of Cain and Abel is more than that of rival brothers. It marks the beginning of a deep rift or antithesis between two groups of people. In Genesis 4 and 5, this antithesis can be traced along family lines; today, it takes the shape of faith versus unbelief.
Because of these roles of Adam and Eve, it is difficult to speak of them as individuals, without speaking more generally about human beings. But that is the point of the Biblical narrative in Gen 1 through 3: in Adam and Eve we see our ancestors and therefore, by representation and example, ourselves.