How would I say "twin sister"?

Question

My understanding is that in Chinese one doesn't say "sister", but always specifies "younger sister" (妹妹) or "older sister" (姐姐). If I had a twin sister, would I refer to her as my 双胞胎妹妹 if I came out first, and as my 双胞胎姐姐 if she came out first?

Obviously I could just say 双胞胎, but I'm asking about cases where I want to specify brother vs sister.

(Searching "twin sister" in Google translate gives 双胞胎姐妹, and searching "I have a twin sister" in gives 我有一个双胞胎妹妹. I suspect that 双胞胎姐妹 would be used for talking about twin sisters generally, and 双胞胎姐姐/妹妹 would be used to refer to a specific person, but I'm not sure, and I don't fully trust Google translate yet)

Answer 1

我有一個双胞胎姐姐/妹妹 is the correct way to mention your older/younger twin sister/brother to others, depends on who was delivered first. Also, a friend will inform others that "她有一個双胞胎姐姐/妹妹" when introducing you to strangers, or "她們是双胞胎姐妹 (same as 她們是双胞胎)" when introducing both of you.

Answer 2

Besides 双胞胎，we have another phrase 孪生. E.g. 孪生兄弟/twin brothers 孪生姐妹/twin sisters etc.

双胞胎姐妹 or 双胞胎兄弟 is fine too. E.g. 他们是一对双胞胎兄弟/姐妹.

If you want to specify one person, you can say 双胞胎(的)姐姐/弟弟. E.g. 我有一个双胞胎的姐姐.