Is it permissible for the cousin (son of paternal aunt) to marry his female cousin (daughter of paternal uncle) if his paternal aunt breastfed one of the girl's sisters, and the girl's mother breastfed one of the cousin's brothers?

There is no impediment to your marriage to your paternal aunt's son, as long as neither of you was suckled by the other's mother. As for your sister who was suckled by your paternal aunt five times, it is impermissible for her to marry any of your paternal aunt's sons. And it is impermissible for your paternal aunt's son who was suckled by your mother five times to marry you or any of your sisters.