Is there some reason why it has to be אחותי rather than האחות שלי?
You can say האחות שלי, but שלי should come after adjectives, giving האחות הקטנה שלי.
I see. I guess I got the order wrong, because I think I put שלי before the adjective.
The word אחות is the only word that I would venture to say EVERY Israeli says in one word (אחותי) and not האחות שלי. Every other word, most people would just say the longer version of the possesive
so בנות means girls as well? from a singular בנה?
The word בת is the singular of בנות, whereas בנה means 'her son'.