Reason: Vivir means to live. Your sentence said mi familia y yo (means my family and I ), so that would be nosotro(a)s form. So it would be Mi familia y yo vivimos en California. I understand this sentence is difficult, but trust me, you'll get used to it :)
Here's some info that would help you later in the future:
Yo vivo Tú vives Ella vive El vive Usted vivan Nosotros vivimos Vosotros vivís
