One way of thinking about this: The FTV is simply the booking that you have just made, stripped of all reservations for flights. It therefore holds the amount that you have paid, including the Amex voucher - and the amount that you have paid can then be used to re-book another trip for the same passengers.

As you probably know, as your Amex vouchers came from the free card, you can only use one on any one booking, for yourself and a travel companion. So your two vouchers will have to be used on two different trips, and you must travel on both trips.