姐妹 Jiemeis (Sisters) are in general, family members or friends of the bride whom are not yet married helping out with the wedding preparations and on the actual day itself. 

姐妹 Jiemeis (Sisters) are commonly more notoriously known for coming up with weird food concoctions for the groom and his 兄弟 Xiongdis (Brothers) during gatecrashing games. 

Other duties and responsibilities of 姐妹 Jiemeis (Sisters) include - 

- overall-in-charge in ensuring flow of programs 

- 'time-keeper'

- hold the train of bride's dress when she walks, get into/out of the car etc

- fuss over the bride, making sure she is comfortable (get her water, wipe any perspiration away etc)

- receptionists during wedding banquet

- emcees during wedding banquet