What is the share of the sole nephew from his elderly aunt's inheritance, given that she has no other heir besides him, and is it permissible for her to bequeath the rest of the estate to someone she raised?

The son of a full sister is considered one of the 'dhawu al-arham' (relatives by kinship), who inherit if there are no 'ashab al-furud' (those with specified shares) or 'asabah' (agnatic heirs). This is the view of the Hanafis, Hanbalis, and the later Maliki and Shafi'i schools.

When alone, the sister's son inherits the entire estate, as he takes the place of the person through whom he is related.

A woman can bequeath up to one-third of her wealth to the person who raised her.