I would say 'The elder brother/sister/sibling' to refer to the oldest of a group of siblings. I suppose that also brings out another point: I would typically use elder only.
An older sister of brothers isn't a good match for you because you'll both fight to become a leader in the relationship. An older sister of sisters is also a poor.
Big Little Brother: A younger sibling who is taller than their older sibling. Black Sheep: A character who doesn't fit in with their family. Blood Brothers: Two people.