What is the Japanese word for sisters?

There's 姉妹 (which incidentally is also read kyoudai, or as shimai) for sisters. There are also other versions that are read the same way but written with different kanji for various sibling configurations (brother and sister, younger brother and older sister, older brother and younger sister). The kyoudai you mention can also just be a generic term for siblings.

Oneesan is the polite term for it, as in if you are referring to another person's older sister. For your own big sister you can say "Ane" or "Oneechan". There's also "shimai", which refers to all of your sisters, older and younger, in one inclusive group.

It will soon enough be "Mei-mei" and "Jie-jie". hahaha

Idk