です/がいます
I wanted to write: My friend's family consists of his father, mother and an elder sister.
私の友達の家族は父と母と姉です。
The sentence below was corrected by a native speaker. However, he could not explain grammatically why he です was inappropriate and changed into がいます。
私の友達の家族は父と母と姉がいます。

Could somebody explain it for me?

Question

です/がいます
I wanted to write: My friend's family consists of his father, mother and an elder sister.
私の友達の家族は父と母と姉です。
The sentence below was corrected by a native speaker. However, he could not explain grammatically why he です was inappropriate and changed into がいます。
私の友達の家族は父と母と姉がいます。

Could somebody explain it for me?

Answer

For me, your original 私の友達の家族は父と母と姉です sounds more natural than your friend's. I think 私の友達の家族構成は父と母と姉です is better.

Answer

just like this。http://www.italki.com/question/259754