Until they married, they were under

Q: My mother and her neighbor lived in one of the furthest villages in the south. My mother gave birth to a baby boy; my neighbor and I gave birth to a baby girl. We grew up believing that we are milk brother and sister (Part No. 18; Page No. 150) as was inculcated by our mothers. I do not know exactly if one of them used to breastfeed and take care of us when the other went to bring water or firewood. We grew up holding this view. My mother was endowed with boys and girls after me, as was our neighbor. My father died as did the father of this girl. Her brother shouldered the responsibly of his family. He waived his responsibilities to me due to his special circumstances. He has legally deputized me according to a document issued by notary public to be a Waliy (a legally accountable person acting for a woman regarding marriage) for any of his daughters who want to marry including his elder sister who is said to be my milk sister. I married her to someone and I also married the second and third girl to those who proposed to marry them. But the third girl had some troubles with her husband. I had to support her as a deputy for her Waliy. During her differences with her husband, my mother told me that I am not really a foster brother for the eldest one of those daughters. I behaved as if I paid her no attention. I went to our neighbor and asked her about what I had heard from my mother. She assured me that I am a milk brother for her eldest daughter. I do not know if our mothers inculcated in our heads the idea of breastfeeding in order not to cause any harm to each other during our childhood or not. (Part No. 18; Page No. 151) The case now is that one of them confirms that we are milk brothers and sisters while the other denies it.Is my conduct, i.e. Marrying those young women to their husbands, is legally valid? Are those young women considered to be my milk sisters? Moreover, there is no blood relationship between my mother and theirs or between their father and ours. Answer my question! May Allah reward you well!