Given the itinerary's timeline, we recommend hiring a car for the group's transportation. A car will offer maximum flexibility and allow you to visit various sites quickly. Expect to spend around $150-$200 for car rental for the weekend.
If you have more time, consider visiting the Exploratorium or checking out one of San Francisco's many hiking trails. Alternatively, if you have less time, consider skipping brunch and booking a sunset boat tour around the bay instead. Another option is to spend an evening in North Beach, enjoying Italian cuisine and checking out the bars in the area.