"They have a shirt."

Translation: Eles têm uma camisa.

[Valestellarium]

Why "elas têm uma camisa" is wrong here?

[Paulenrique]

Also right.

[baji05]

Here its not mentioned as blouse. So only option2 is correct

[maiaracastro19]

Shirt means camisa, blouse means blusa. Blusa is a feminine clothe, camisa can be used by men and women.