These two girls are my sisters: Cindy and Halen.→这两个女孩是我的妹妹辛迪和海伦
(these two girls are my families)cindy is my sisiter and Halen is my cousin。→(这两个女孩是我家人)辛迪是我妹妹 海伦是我表姐
ps:你的句子有问题吧 两个女孩是我的妹妹 后面怎么又来个表姐了?
These two girls are my sister Cindy and cousin Helen