I see. That can indeed be very bad. I suppose the fare difference is about USD300 between V and N. With a $200 penalty per ticket, that will cost a family of four an additional USD4x(300+200)=2000, which may be more than half of your current N ticket.

I don't know how full they are. If not too full, they may release some N fares the last few days, but that can be a huge gamble. The flights may also be so sold out that only the highest fares are available.