The "et"'s are parsed slightly differently in Yebamot 62a where the two "et"'s in Gen. 4:2 indicate Cain and his sister, and Abel and his (one) sister.
ðə "ˈɛt"ˈɛs ɑːɹ pˈɑːɹst slˈaɪtli dˈɪfɹəntli ɪn jˈɛbɐmˌɑːt sˈɪksti tˈuː ˈeɪ wˌɛɹ ðə tˈuː "ˈɛt"ˈɛs ɪn dʒˈɛn. fˈoːɹ:tˈuː ˈɪndᵻkˌeɪt kˈeɪn ænd hɪz sˈɪstɚ, ænd ˈeɪbəl ænd hɪz wˈʌn sˈɪstɚ.