Is it permissible for the elder brother to marry his maternal uncle's daughter, whom his mother breastfed along with his younger brother?

It is not permissible for you to marry your cousin (daughter of your maternal uncle) because she was suckled by your mother, thus becoming your sister through breastfeeding. It is forbidden for you to marry her, based on the Almighty’s saying: "And your sisters through suckling" (Quran 4:23), and the Prophet, peace and blessings be upon him, said: "What is forbidden by lineage is also forbidden by suckling." As for her other sister, it is permissible for you to marry her.