The verse in question is;
“O sister of Aaron! Thy father was not a man of evil, nor thy mother a woman unchaste!” (Al-Qur’an 19:28)
It does not mean that here Qur’an calls Mary, the real sister of Aaron, the Prophet who was hundreds of years before her. Here she is only being called a female person of the family, from the Noble lineage of Prophet Aaron.
The Qur’anic usage:
In order to understand Qur’anic language one must look into other Qur’anic passages.
Qur’ans calls Prophet Shoaib as the brother of the people of Midian. Qur’an says;
“And unto Midian (We sent) their brother, Shu’eyb.” (Al-Qur’an 7:85)
And similarly Qur’an calls Prophet Salih, the brother of the people of Thamud. It says;
“And unto Thamud (We sent) their brother Salih.” (Al-Qur’an 11:61) Read more of this post