The breastfeeding mother dying and another woman ascertaining the breastfeeding

Q: I am a 20-year old man and my sister is twelve years old. The son of my paternal uncle who is eighteen years old proposed to my sister, and I accepted and concluded their marriage contract. Likewise, I proposed to his sister who is ten years old and concluded her marriage contract. Neither the son of my paternal uncle nor I have consummated our marriage yet. Both of us will pay an agreed-upon Mahr (mandatory gift to a bride from her groom) and the bridal gold and follow the marriage procedures that are common among Muslims. Recently, my paternal uncle's wife said that my late mother breastfed her daughters and my sisters together. I do not know if the saying of my paternal uncle's wife is true or not and whether my mother breastfed her daughters or not. Is it prohibited for us to marry each other's sisters? How is their daughter prohibited to marry me? And how is my sister permitted to marry their son? Please, advise. May Allah reward you with the best!

A: Breastfeeding that prohibits marriage must occur five times or more during the first two years of the baby's life. When the baby takes the breast and sucks milk from it, it will count as one time of breastfeeding. Thus, if the daughter of your paternal uncle is proven to be breastfed by (Part No. 21; Page No. 58) your mother five times or more as stated above, it will be prohibited for you to marry her because she is considered your foster sister. Allah (Praised and Exalted be He) says: Forbidden to you (for marriage) are: your mothers, your daughters to His saying: ...your foster milk suckling sisters He (Exalted be He) also says: The mothers shall give suck to their children for two whole years, (that is) for those (parents) who desire to complete the term of suckling The Prophet (peace be upon him) said: Milk relationships are equal to blood relationships in rendering marriage unlawful, i.e. whatever is prohibited due to blood relationships is also prohibited by milk relationships. Agreed upon by Al-Bukhari and Muslim. Furthermore, it was authentically reported on the authority of `Aishah (may Allah be pleased with her) that she said: It was among the revelation of the Qur'an that ten known times of breastfeeding make the marriage prohibited, but this was later abrogated and reduced to five. The Messenger of Allah (peace be upon him) died and the ruling remained effective. If your mother breastfed this girl less than five times or after the age of two years old, it would be permissible for you to marry her. What the wife of your paternal uncle said in this regard is accepted if she is trustworthy. However, the son of your paternal uncle will be permitted to marry your sister in question if they did not undergo breastfeeding that makes marriage unlawful. His sister's breastfeeding from your mother, being little or much, does not affect his marriage to your sister. If the wife of your paternal uncle is not trustworthy or does not remember the numbers of breastfeeding times, whether they were five or more or less, her testimony will be (Part No. 21; Page No. 59) of no significance.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.