Is it permissible to marry the daughter of the maternal aunt, given that the grandmother mentioned she breastfed her along with the questioner's maternal uncle, while the grandmother does not recall if there was milk or the quantity of the breastfeeding?

If the grandmother doubts the number of sucklings or the presence of milk, then the prohibition is not established, because the default is its absence, and doubt does not remove certainty. Nevertheless, it is said that it is better to refrain from marriage as a precautionary measure and to avoid doubtful matters.