Depending on the airline, even if you cancel, the rebooking can only be done for the original passenger.
SWA is an exception to this. You could book you and your son. And then if your son didn't go, cancel and you would get ticketless travel funds, that would then be used to book you and your husband.
I'm not familiar with alot of the other discount carriers, so not sure of their rules.
Either way, I'd book you and your son on different confirmation numbers to ease and cancellation you may decide to do.