1. 姐妹 (jiě mèi): This is the most common way to say "sisters" and refers to both older and younger sisters. It literally translates to "elder sister" and "younger sister".
2. 姊妹 (zǐ mèi): This is a slightly less common way to say "sisters" and is usually used when referring to sisters in a more formal context. It also translates to "elder sister" and "younger sister".
Both words can be used interchangeably in most cases, but "姐妹" is more commonly used in everyday conversation.