What is the ruling regarding the brothers of a milk-brother? Are they treated the same as a milk-brother, or are they considered strangers? Is it permissible to uncover one's face in front of them?

What is established by lineage is also established by fosterage. So, whoever breastfeeds from a woman becomes a son to her and to her husband, the owner of the milk. If you shared fosterage with your cousin from his mother (your aunt) or his father's wife, then he and all his siblings become your foster siblings. However, if he shared fosterage with you from your mother or another woman, then the prohibitory relationship is specific to him alone, without his siblings, unless they also shared fosterage from the same woman.

If they are not your mahrams, you must observe full hijab in front of them. However, if they are your foster brothers, you are not required to wear hijab, and they are permitted to see what a man may see of his mahrams, such as the head, neck, hands, and feet. Seclusion and handshaking are permissible without suspicion.

The fosterage that establishes prohibition is that which occurred within the first two years of life and consisted of five satisfying breastfeedings.