Are the sisters of the paternal female cousin (S) - who has become a sister through suckling - also sisters to the questioner?

First: Fosterage does not extend to the relatives of the suckled child, such as their siblings. Therefore, you are not a brother to the sisters of your cousin (S) through fosterage.

Second: Your suckling from your grandmother makes you a brother to your mother and your maternal aunt through fosterage. Consequently, you become a maternal uncle to all the daughters of your maternal aunts through fosterage, and they are forbidden to you. As for whoever suckled from your grandmother, she has become your sister through fosterage. Ibn Baz, may Allah have mercy on him, mentioned that if a child suckles from their grandmother five times or more, they become a brother to their maternal uncles and aunts, an paternal uncle to the children of their maternal uncles, and a maternal uncle to the children of their maternal aunts. Therefore, it is not permissible for him to marry the daughters of his maternal uncles or aunts.