In Bereshit Rabbah (22:2), a discussion of Gen. 4:1 ff. has Rabbi Yehoshua ben Korcha mentioning that Cain was born with a twin sister, and Abel with two twin sisters.
ɪn bˈɛɹɪʃˌɪt ɹˈæbə twˈɛnti tˈuː:tˈuː, ɐ dɪskˈʌʃən ʌv dʒˈɛn. fˈoːɹ:wˈʌn ˌɛfˈɛf. hɐz ɹˈæbaɪ jɛhˈɑːʃjuːə bˈɛn kˈoːɹtʃə mˈɛnʃənɪŋ ðæt kˈeɪn wʌz bˈɔːɹn wɪð ɐ twˈɪn sˈɪstɚ, ænd ˈeɪbəl wɪð tˈuː twˈɪn sˈɪstɚz.