No, it could work. Huge and big are synonyms in English, so if you were translating that would be acceptable.
Big = Grande
Huge = Enorme
I'm not trying to tell you you're wrong, I'm just informing you that the most used term for this is "grande".
Because that would mean in English : "My family are big", and that isn't proper grammar (which Duolingo is all over), and doesn't make much sense. Did that answer your question?
Instead of saying "my family is big", why can't you just say "my big family"? They both refer to the same thing.
Well, that'd be mi familia grande, rather than mi familia es grande. The first is a noun phrase and can be used as following: "I like my big family/Me gusta mi familia grande" while the second is a sentence on its own right.
I'm not a native speaker of Spanish, though, so I don't know if the grammar on the Spanish sentences are right or not.
"Mi familia es grande," is describing the family as big. If you just say "My big family," that's either counted as slang or incorrect altoghether. I hope that clears the confusion.
Troll. Keep your nasty comments in your head. Try avoid hurting others feelings, if you can't please stop using Duolingo.