The Role Of The Twins In John Steinbeck's East Of Eden

As Samuel points out in East of Eden, we are all Cain’s children. Since Cain killed his brother Abel, Abel did not have any children and the humanity continued with Cain. He left Eden, he settled down in a land called Nod, which was East of Eden, where he met his wife, who gave him his first son Enoch.
Although in the first generation of the Trasks, it is Abel-like character, Adam who goes to California with pregnant Cathy and their two twins are later born, there is from a beginning a strong reason to doubt whether the twins are actually Adam’s. Cathy as we know slept with both of brothers at the same time, to be more precise, she had sex with Charles first and Adam second, so the twins could easily be the children of Charles. This question