Is it permissible to marry the daughter of a paternal aunt if the mother had breastfed the paternal aunt's son several times?

As long as your cousin (daughter of your paternal aunt) was not suckled by your mother, and you were not suckled by her mother, and neither of you were suckled by another woman, then there is no legal impediment to marrying her. This is because there is no blood relation, foster relation, or any other factor that would prevent the marriage. Your mother suckling your paternal aunt's son does not affect marriage to his sister. However, this son becomes a brother to all your sisters, and it is not permissible for him to marry any of them, due to the Prophet's (peace and blessings be upon him) saying: "Suckling makes unlawful what lineage makes unlawful."