Doubt as to whether breastfeeding took place
Question

                My maternal aunt breastfed my brother, who is older than me. Now he is the brother of my maternal cousins. My aunt used to put us to her breast to nurse us, and according to what she said (may Allaah have mercy on her) no milk came out. Since we were small and until now we interact with them on the basis that they are our siblings, and no marriages have taken place between us because we are regarded as siblings. Please advise us, may Allaah reward you with good.
Praise be to Allah.
    Firstly: 

    The breastfeeding by which the relationship of mahram is 
    achieved is subject to two conditions: 

    1 – That there should have been five or more feedings

    2 – That it should have taken place within the first two 
    years of life, before weaning. 

    See the answer to question no.
    40226 for more information on these 
    two conditions. 

    It is not stipulated that the child should have drunk his 
    fill of milk, rather taking in the nipple and sucking milk is regarded as 
    breastfeeding. 

    If the child takes in the nipple but no milk comes out, that 
    is not breastfeeding, and does not mean anything. 

    It says in al-Fataawa al-Hindiyyah (1/104): Because 
    when the milk comes out, breastfeeding takes place, otherwise it does not. 
    End quote. 

    In Fataawa al-Lajnah al-Daa’imah (21/53) it says: If 
    your mother gave the breast to your paternal uncle to keep him quiet, and he 
    did not receive any milk from her breast, then there is no relationship of 
    mahram, and the marriage is permissible. End quote. 

    Secondly: 

    If there is any doubt as to the number of breastfeedings, or 
    whether breastfeeding took place, then the relationship of mahram cannot be 
    proven. 

    The scholars of the Standing Committee were asked: 

    I have a female cousin (the daughter of my maternal aunt) and 
    I want to marry her, but the problem is that that there is some doubt 
    concerning our relationship through breastfeeding, as breastfeeding was 
    shared between my grandmother (the mother of my mother) and her mother. But 
    this grandmother is not sure about this breastfeeding. We asked her and she 
    said, “I don’t know, I have forgotten. If this girl breastfed from me, there 
    was no milk then.” This is what the grandmother says. I hope that you can 
    find a proper solution for me; is marriage to her permissible or not, based 
    on what the grandmother says? 

    They replied: 
If the situation is as 
    described, then you may marry the cousin whom you mentioned, because 
    breastfeeding concerning which there is some doubt does not have any effect. 
    Rather the relationship of mahram through breastfeeding is only established 
    if there were five or more breastfeedings, during the first two years of 
    life. If it is not known, then the basic principle is that this marriage is 
    permissible. End quote. 

    Fataawa al-Lajnah al-Daa’imah, 
    21/133 

    See also question no. 804 

    Based on this, your brother who it is proven breastfed from 
    your maternal aunt is a son to her through breastfeeding, and is a brother 
    to all her children. 

    But in your case there is no proof that the relationship of 
    mahram was established because there is some doubt and hesitation with 
    regard to breastfeeding. 

    And Allaah knows best.