"Your family is not small."
Translation:Twoja rodzina nie jest mała.
You can say: "Twoja rodzina to nie (jest)" + [noun in nominative]. But with an adjective you should use conjugated "to be". In some contexts you could add "to" but it would be some kind of emphasizer. For example you could say: "Ty to jesteś taki głupi" (You are SO dumb) or "Twoja rodzina to nie jest wcale taka mała" (Your family is not so small at all (as you mentioned or as I thought)). And it's rather casual speech.
Twoja is feminine singular, twoje is neuter singular or non-masculine-personal (other) plural.