This is the 7482nd most frequent Japanese word.
兄弟
"Brothers" or "siblings" (general term for brothers and/or sisters).
Here, '兄弟' is used to refer to siblings in general, encompassing brothers and/or sisters.
私には兄弟が二人います。
I have two siblings.
In this context, '兄弟' specifies one individual within the group of brothers specifically, inferred by the broader context.
彼は私の兄弟の一人です。
He is one of my brothers.
Here, '兄弟' is used in a conceptual manner, referring to bonds between brothers or sibling relationships in general.