Cain's wife was his twin sister who had been born along with him in the Garden. What, you one of those people who believes there were other human beings around other than those descended from Adam?
Genesis 4:22 says "the sister of Tuval-Qayin was Na`amah." She was thus the daughter of Lamekh, the descendant of Cain.
One opinion is that this is the Na`amah that Noach married. Another is that Noach's wife was named Na`amah, but she wasn't the same person as Tuval-Qayin's sister.
According to the scientific community upon the discovery of DNA is it literally impossible for all God's children to have come from 'the' Adam and Eve. And Moses records there were two different days of creation. The sixth day and then the 'day' following the seventh. So your attempt to label and impugned for what Moses recorded is NOT lost.
There is NO record of Cain having a twin sister but a twin brother Able which Cain murdered.
Genesis 4:22 says "the sister of Tuval-Qayin was Na`amah." She was thus the daughter of Lamekh, the descendant of Cain. One opinion is that this is the Na`amah that Noach married. Another is that Noach's wife was named Na`amah, but she wasn't the same person as Tuval-Qayin's sister.
Genesis 4:17-23 does indeed give Cain's genealogy, but Genesis 5 gives 'the' Adam's genealogy, and the names are curiously similar but they are not the same.