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)