Why do the forgotten books of Eden mention Cain and Abel had sisters/Adam and Eve daughters?
5 And God looked at His maid-servant Eve, and delivered her, and she brought forth her first-born son, and with him a daughter.
6 Then Adam rejoiced at Eve's deliverance, and also over the children she had borne him. And Adam ministered unto Eve in the cave, until the end of eight days; when they named the son Cain, and the daughter Luluwa.
7 The meaning of Cain is "hater," because he hated his sister in their mother's womb; ere they came out of it. Therefore did Adam name him Cain.
8 But Luluwa means "beautiful," because she was more beautiful than her mother.
11 When the days of nursing the children were ended, Eve again conceived, and when her days were accomplished she brought forth another son and daughter; and they named the son Abel, and the daughter Aklia.
http://www.sacred-texts.com/bib/fbe/fbe080.htm - The First Book of Adam and Eve
And the Book of Jubilees -
IV. And in the third week in the second jubilee
she gave birth to Cain, and in the fourth she gave birth
to Abel, and in the fifth she gave birth to her daughter
51:3 i.e. "iniquity" (Heb. ’āwen). Another daughter, ’Azûrâ (= "well guarded"), was born later. Cain married ’Âwân and Seth ’Azûrâ. There is great divergence as to these names in later writers . According to Pirḳe de R. Eliezer, Cain's wife was his twin-sister (xxi.).
http://www.sacred-texts.com/bib/jub/jub16.htm - The Book of Jubilees
Where did this originate, that Adam and Eve had daughters and Cain and Abel sisters?
Where is the origin of this?
I mean,we disregard that Cain and Abel had sisters as non-Scriptural? Why are these Characters in the forgotten books of Eden and the book of Jubilees?