The Friends of the Uffizi card worked really well for my husband and I: highly recommend!
We bought ours at the welcome desk at the Uffizi when we got into Florence:
http://www.amicidegliuffizi.it/diventa_socio.php?pg=8&ln=en
Your one problem is that it only covers two adults and children under the age of 18. If one of your teens is 18 or older, you'd need to purchase an additional youth pass for € 40,00. This is still a big savings over the €72 euro pp Firenze Card (if that's what you are comparing).
This pass is especially nice if you're going to be in Florence for over 3 days and, unlike the Firenze card, allows multiple visits to any of the attractions it covers: nice for breaking a large museum into 2 visits if desired. Do be aware, though, that it doesn't cover entry fees to every attraction - such as Santa Croce or the Baptistry at the Duomo. Even paying for those things individually, you'll still come out ahead, though. Florence is such a walkable city that we wouldn't not have even used the transport piece of the Firenze Card.