"I do not have a sister, but I have an older brother."

Translation: Saya tidak punya saudari, tapi saya punya seorang abang.

[Nestor-Evan]

Saya tidak punya seorang saudari, tapi punya abang.

What is wrong with the above sentence?

[octavzlatior]

My understanding is that you use seorang when you want to be specific about the number (like when you use the article a/an in English). Your sentence could also mean 'I have more brothers'

[UltraSlacker]

I put seorang before saudari, why is it incorrect?

[Ankojem]

I think that : "Saya tidak punya saudari, tapi saya punya seorang saudara abang"
is little bit normal sentence... or no?

[adi._]

no,

kakak = older brother or older sister

adik = younger brother or younger sister

abang = older brother