"That is her family."
If I'm correct, nage is usually used for one specific thing, like, "nage ren shi women de yisheng (THat is our doctor)" and na is used for a more general thing, like a family.
In my Chinese classes in school, I was taught that in cases where the genetive noun was "close" or especially attached to the object of possession (like a person to his or her family), the 的 was often omitted and the possessive was implied. Is this a common practice in written Chinese, and should I report it as a potential correct answer?
ge 个 is measure word, which would be used in Chinese. There are many other measure words. You just have to learn it I'm afraid. I'm from Hong Kong by the way.
I think if you use 个 it will sound weird something like that is her one family. :v
I dodn't need that to say "my doctor" or "your teacher", so why do I need it for a family
Why not '那个家人是他的。'? Or is 'that family is hers' to far off from the original sentence?