He was breastfed by the wife of his paternal uncle; are the daughters of his paternal uncle from his other wife forbidden to him for marriage?
Question

                I have a paternal uncle who is married to two wives, one of whom breastfed me. Is it possible for me to marry the daughters of the other wife?.
Praise be to Allah.If you were breastfed five 
    times in the first two years of life by your uncle’s wife, then she is your 
    mother through breastfeeding and your uncle is your father, and all his sons 
    and daughters from this wife and from all his wives are brothers and sisters 
    to you.  
Based on that, the 
    daughters you asked about, if they are your uncle’s daughters, are mahrams 
    to you; if they were from another husband, someone other than your uncle, 
    then there is nothing wrong with you marrying one of them. 
Shaykh Ibn Baaz (may Allaah 
    have mercy on him) said: If a woman breastfeeds a child five times within 
    the first two years, or more than five times, the infant becomes a son to 
    her and her husband, who is the “owner of the milk”, and all the children of 
    the woman from the husband who is “the owner of the milk” or another husband 
    become brothers and sisters of the infant, and the children of the husband 
    who is the “owner of the milk”, from the wife who breastfeeds and other 
    wives, become brothers and sisters of the infant who is nursed. End quote 
    from Majmoo’ Fataawa Ibn Baaz (22/274). 
He was also asked (may 
    Allaah have mercy on him): I was breastfed by a woman, then her husband took 
    another wife and that wife had children; are they brothers to me? 
He replied: If you were 
    breastfed five or more times and the milk was attributed to the husband 
    because it resulted from a pregnancy that occurred due to him, then they are 
    your brothers through your father and your mother through breastfeeding. As 
    for the children from his second wife, they are brothers to you through your 
    father through breastfeeding. End quote from Fataawa al-Shaykh Ibn Baaz 
    (22/305). 
And Allaah knows best.