What is the ruling on breastfeeding a male cousin, given that each of them was breastfed by his own aunt separately, and are these few breastfeedings considered prohibitory by reason of suckling?

If you and your maternal cousin were suckled by the same woman with five known full feedings, then you are foster brothers. However, if the feedings were fewer than five, scholars have differed. Some are of the view that a single feeding establishes the prohibition, while others – and this is the most preponderant view – hold that the prohibition is not established except with five known feedings, based on the Hadith (definition) of Aisha (may Allah be pleased with her). Accordingly, if your maternal cousin did not receive five full and satisfying feedings, he is not considered your brother Islamically, and you must observe hijab (definition) from him.