Was Our Lady Mary, peace be upon her, the only child of her parents? If so, how then could Christ and John, peace be upon them, be cousins?

Imran married Hannah, and they had Mary. Zakariya married Ishaa‘ and they had Yahya (John). There are two opinions regarding Ishaa‘, the mother of Yahya:

1. The majority believe she was Mary's sister. Thus, Jesus and John would be true maternal cousins. They cite the Hadith of the Mi'raj (Ascension): "Then, behold, Yahya (John) and Isa (Jesus), who are maternal cousins." 2. Ibn Ishaq and Ibn Jarir believe she was the sister of Mary's mother (Hannah). In this case, she would be Mary's maternal aunt. Therefore, Jesus and John would be maternal cousins metaphorically, because a mother's maternal aunt is considered like a maternal aunt, or because the term "sister" can be applied to a niece. This view is supported by the fact that Hannah, the wife of Imran, was barren then conceived Mary by Allah's permission, which suggests she did not have sisters with daughters of childbearing age.