Is it permissible for your foster sister's brothers to see your face while you are veiled?

Whoever shared suckling with you from the breast of one woman — whether she was your mother, their mother, or another woman — is your brother through suckling. As for whoever did not share suckling with you from one woman, he is a stranger to you, and you must observe hijab in front of him. You have no relation to whoever suckled with your sister unless you also suckled with him.