The exercise was to translate: "we are 6 in my family" The answer given is: "watashi no kazoku wa roku-nin kazoku desu"
I can understand the role of all words except for the second occurrence of kazoku. As far as I can tell the sentence is complete without it.. "Watashi no kazoku" = "my family" "Wa roku-nin" = "has 6 people"
Perhaps I am misunderstanding the way the nin counter is used?
(If anyone uses Japanese characters in the reply... I can only read hirigana)