What you are talking about is non-reving a flight. Most airlines allow your family to fly for free or for a small fee. In addition to you flying for free, your family which includes your wife or companion, children under 21, and mother and father all fly for free on my airline. Depending on your airline some have agreements with other airlines to travel for free or for a discounted fare. The legacy carriers generally don't participate. Don't forget this is all stand-by, so hopefully there are a few open seats. In addition to what BRI85 said you are always lower than paying passengers when flying stand-by at least at every airline I've worked.