I also reported this 4 years since your comments. In English a family are, by definition, made up of more than one person, so 'is' is never correct as you are always referring to 'they'. The phrase ''They is" will and can never be correct.
To further elaborate, "dove la tua famiglia?" is not a complete sentence as there is no verb; it would translate to "Where your family?" "Dove" is just "where" and "dov'è" is a contraction of "dove è" meaning "where is."