It will be impermissible for a person who was breast-fed by his Dadi (paternal grandmother) to get married to his paternal uncle’s children. (Fataawa Mahmudiyyah Vol. 11 Pg. 340) 

The reason of impermissibility here is because after both have been breast-fed by the same woman, the person and the paternal uncle have become foster brothers/sisters. Just as a person is not allowed to marry his real brother’s/sister’s children (Fataawa Mahmudiyyah Vol. 11 Pg. 301), in the same manner, a person has been forbidden to marry his foster brother’s/sister’s children. (Majma'ul Anhur Vol. 1 Pg. 376) 

AND ALLAH TA'AALA ALONE IN HIS INFINITE KNOWLEDGE KNOWS BEST

ANSWERED BY: Zaid Mahammad 

CHECKED AND APPROVED BY: Mufti Muhammed Saeed Motara Saheb D.B. 

Islamic Date:10 Jumaadal Ula 1440 - English Date: 17 January 2019