It's a Spanish phrase that uses the possessive pronoun "su" (his/her/their) and the noun "hermano" (brother).
To understand the gender, you need to know the context and who is being referred to.
* If the speaker is male: "Su hermano" refers to the brother of a *female* person being talked about.
* If the speaker is female: "Su hermano" refers to the brother of a *male* person being talked about.
Examples:
* "Su hermano es médico." (His brother is a doctor.) - This refers to the brother of a woman.
* "Su hermano está en la escuela." (Her brother is at school.) - This refers to the brother of a man.