Your trip sounds fabulous!!! You are going to have a wonderful time. Dh and I moved to the Bay area in November 2002 and have been to Napa and Sonoma many many times. Too many to count. WE LOVE IT.
Where in Napa are you staying? If you let me know that, I would probably be able to steer you to a restaurant.
Since there are so many of you, you might want to think about renting a little tour bus. That way you wouldn't have to worry about driving.
You should also think about taking a hop over to Sonoma county - not too far, and is a lot less snooty in general then Napa is. Much more informal.
Many of the wineries in Sonoma don't charge for tasting - most of the ones I have been to in Napa do (the only one that comes to mind that doesn't is V. Sattui.) All of those tasting fees really add up so you might want to keep that in mind.
We have been to tons of wineries - I can send you more info later after I find out where you will be located, (and I have to run now anyway) but here are c couple of our favorites
Artesa: great wine, and its way up on a hill. Pinot noir and chardonnay are great here. You can see for miles and on a clear day, even see San Francisco! Very cool but slightly snooty. I think we paid $6 for tasting.
Gundlach Bundschu: This is a great place for a picnic. I really recommend it - we love it so much we joined their wine and social club. It's really informal and fun, free tasting and excellent wines. This may very well be our favorite winery. Also great is their sister winery, Bartholomew Park - Bartholomew Park has a great(and sort of crazy) history and a little museum.
V. Sattui: Although there wines are no particulary spectacular, it is a fun place. Free tasting and a great deli. The Sattui family red is a great picnic wine.
Domaine Carneros: Kind of pricey - but its in a castle. Although you would think it would be snooty, it really wasn't. You don't actually do tastings here - you get a table on the verandah of the castle and order sparkling wine (its GOOD) and they bring you crackers and spread. You can also order chocolates!
I will write more later, when I get home!