Will Mabrouk, who was nursed five satisfying nursings by the grandfather’s second wife, become a brother to the grandfather’s daughters from his first wife, and is it permissible for the questioner’s sisters (daughters of the grandfather’s son from his first wife) to enter upon him?

A person who nurses from the milk of a man's wife becomes a brother to all of that man's children, for fosterage (rada'a) in this context is equivalent to lineage (nasab). And this father's sisters and his daughters' daughters are considered unmarriageable (mahram) to the suckled person, based on the Prophet's (peace be upon him) saying: "Indeed, fosterage prohibits what birth prohibits."