Can Breast Milk Be Poisonous Leading To Death In A New Born Child?

My grandmother had 11 children but one after the other were dying within months of their birth. It was only my aunt who had survived. My father was born (number 12th child in the house). At his birth the midwife advised my grandparents that -the milk of my grandmother might be poisonous for baby and my grandparents sought help from friends to find a mother who can breastfeed their son (my father). a mother from other faith was found and she nursed my father like her own son. My father and grandparents are all gone but during funeral of my sister in January, 2011, my cousin (the eldest son of my late aunt) mentioned this in one of the family gatherings. We all know about this but since it came back down the memory lane, I was wondering to know, what could have been the cause for those deaths? Can mother milk be poisonous? Also, I would now like to visit Pakistan, the ancestral town of my parents/grandparents/greatgrandparents.. to find the family that helped our grandparents. We are Hindus and had to leave Pakistan at the time of partition in 1947, and the lady that breastfed my father was a muslim. Both aspects are important to me now. Regards