In south asia people don't address their elder brother and sister by name it is considered disrespectful. Their are formal and informal pronouns as well. We never adress elders by name. We have certain titles that conveys affection and respect for example putting jan(dearest) after brother and sister. I think this is common in Chinese and Japanese culture as well.

I just would normally state the following: I have one older brother and two younger twin brothers.

If necessary, I would also supply the names of my brothers if the specific brother would need to be identified. If we talk to each other, we might use the term "Brother" or we would simply use the appropriate name.

There is only "older brother/s" or "older sister/s"

Or we can say elder brother/s elder sister/s.

For younger brother/s sister/s we can also the the youngest brother/sister.

For older brother/s sister/s we an also say the eldest.

We do not have a specific word to indicate "elder brother" [ağabey] in English, it is only occasionally we might distinguish between elder and younger brother. Usually if someone specifically asks, otherwise when speaking to them it's just by their first names