Bill, you truly are a scholar and a gentleman...
That's an amazing offer, you are certifiably insane!
It would take you something like 1 &1/2 to 2 hours minimum to make an Oakland to Fairfax roundtrip , and you're offering to do it 2 times in one day? (I do need to get back, obviously) That's incredibly generous of you, thanks for the offer, my friend.
I'd hate to put you through that much trouble. I'm thinking that I might be able to do 5 or 6. Two hard cases and 3 or 4 well-padded gig bags maybe. I'll do a trial 'load' and see how it looks.
Then there's amplification...no way I'm bringing a cab if I bring the basses & guitar but I hope & believe there will be enough to go around basswise & guitarwise.
Valentino