Ride on the Cablecars, Alcatraz is fantastic, Fishermans Warf (A bit touristy but worth a look. you get the ferry to Alcatraz from there), Shopping in Union Square. Eating places there are loads, I can't recall the names, there was a Mexican place that did proper mexican food, if I can find the name I will come back with it. We just loved San Francisco.
The Napa Valley, once again there are so many wineries. If they go into the tourist board there they will give them a map and recommend the best ones to see. If they can get a reservation for - THE LAUNDRY - a Restaurant in Yountville, that is supposed to be really good. We couldn't get a reservation.
They will have a fantastic time I am really envious.