What is the ruling on breastfeeding between the eldest sister and the maternal cousin's daughter, given that the mother breastfed the maternal cousin's son, and the maternal cousin breastfed the eldest sister? Are all the maternal cousin's children considered brothers and sisters through breastfeeding? Is it permissible to be named "Abd al-Mahdi" and "Abd al-Nasir," and must those who are named thus change their names?

All those who nursed from the same woman's breast are milk-siblings, even if the time between their nursings was long. Your mother is considered a mother to your aunt's son and daughter who nursed from her, and they are siblings to you and your siblings. This does not include the rest of your aunt's children. Your aunt is a mother to your eldest sister through nursing, and therefore your eldest sister is a sister to all of your aunt's children. This ruling does not apply to you and your other siblings. All relatives of the nursing woman and the man to whom the pregnancy is attributed become relatives of the nursed child in terms of prohibition, because the milk is created from their fluid. It is not permissible to be named 'Abd al-Mahdi, nor 'Abd al-Nasir.