"I do not have sisters."
Translation:Benim kız kardeşim yok.
Many thanks for the reply. My comment, however, was not about the differences between brother, sister, older brother, and older sister, but about the use of the plural suffix with "kardeş-im" in the above sentence. As far as I can remember, I wrote "benim kız kardeşLERim yok" and that was counted wrong. So I wanted to be sure, whether/why putting a plural suffix here is wrong, especially that the English sentence had "sisters" (in the plural).
In English one can either say "I do not have A sister" or "I do not have sisterS", which do not mean exactly the same thing, but very close in meaning. I wonder whether in Turkish one translate these two sentences as "benim kız kardeşim yok" and ""Benim kız kardeşLERim yok" respectively
var does not mean "have", and yok does not mean "not have".
They mean something like "exist" and "not exist" -- and the way Turkish says "I have a sister" is "My sister exists" (Benim kız kardeşim var) and "I do not have a sister" is "My sister does not exist" (Benim kız kardeşim yok).
So you need benim rather than ben for the same reason that "I sister does not exist" does not work.