Is the elder daughter of the questioner forbidden to her sister's son if her sister breastfeeds the questioner's infant son, knowing that the questioner's elder daughter is two years and four months old? And is it permissible for the questioner's sister to breastfeed the questioner's elder daughter so that she becomes a foster sister to her son? And is it permissible for the questioner to take hormones or pills to produce milk to breastfeed her sister's son? And does this suckling achieve the prohibition of suckling? And if the questioner extracts milk and gives it to her sister's infant son, is it considered suckling, or must it be suckled directly from the breast for the questioner's son to become a foster son?

If your sister breastfeeds your son while he is under two years old, he becomes her son through fosterage and a brother to her children. It is permissible for your sister's son to marry your daughter because your daughter is not a sister to your sister's children.

Prohibitive fosterage is that which occurs within the first two years of the child's life; anything after that does not establish prohibition.

Based on this, if your sister breastfeeds your daughter after your daughter has passed the age of two years, it does not prohibit her to your sister's son.

Milk produced as a result of taking medication establishes prohibition. So, if you breastfeed your sister's son with this milk, you become his mother through fosterage.

It is not a condition for the establishment of fosterage prohibition that the child suckle directly from the breast. If the milk is given to the child by any means (such as an injection or a container), it establishes the prohibition.