Are the older brothers of one's milk-sibling considered brothers, and is it obligatory to observe Hijab in front of them?

If the suckling was from the questioner's mother, then his brotherhood is limited to the brother who shared the suckling with him. However, if the suckling was from the brother's mother, then all of her children are brothers and sisters to the questioner, according to the Almighty's saying: "and your sisters from suckling."