Is it permissible to marry the daughter of a paternal uncle's son if her elder sister was nursed by the younger brother?

"Suckling establishes the same prohibitions as lineage; thus, what is prohibited by lineage is also prohibited by suckling. Whoever suckles from a woman becomes her child and the child of her husband, the owner of the milk. This applies specifically to the suckled child, not to his siblings.

Based on this, your younger brother suckling with the sister of your paternal cousin's daughter does not make her unlawful for you. She would not be unlawful for you even if her sister had suckled with you. She would only be unlawful for you if her sister were your suckling sister, meaning that you and she shared suckling from one woman, or if you both suckled from two women from the milk of one man, or if she were your paternal aunt, maternal aunt, niece, or nephew's daughter through suckling. In all other cases, she is not unlawful for you.

It is important to note that the suckling which establishes prohibition must consist of five full, satisfying sucklings, according to the preponderant opinion."