What is the ruling on marrying the daughter of a maternal aunt, and is the maternal aunt considered a sister through breastfeeding if the mother left her son with her for 15 days during the breastfeeding period?

If a person is nursed by his grandmother with five full breastfeedings, he becomes her son through suckling and a brother to all her children, male and female. It becomes unlawful for him to marry any individual from her descendants; he is a maternal uncle to the daughters of her daughters and a paternal uncle to the daughters of her sons. Consequently, he is not permitted to marry his maternal cousin if she is a daughter of the aforementioned grandmother.