1. I did multiple waitlisting for my wife before, but I do not what the current rule is. However, there is no point to waitlist on a flight you cannot get or do not have an underlying ticket. You should change your waitlist to the other flight.

2. You can redo waitlisting again. My feeling is that CX will release availability 2-3 days ahead. You can also try to do instant upgrade at SFO when you check in.