It depends if you think of the family as a unit. If you do, then use the singular "wasn't."
But if you think of the family as a collection of individuals, then you can think of the word as a plural, and use "weren't."
Americans tend to use the singular for these situations (same with "company" or "firm," etc.). I've been led to believe that in other places the plural is more com
Americans tend to use the singular for these situations (same with "company" or "firm," etc.). I've been led to believe that in other places the plural is more common than it is here.
I don't know about English in other countries, but I've read that in BrE both singular and plural verbs can be used.