Thanks all, they said it was an FAA restriction. One option was to disconnect and drop the last leg of the original ticket, get a credit and repurchase the last let separately, but my wife and I are travelling separately with our two kids on two companion fares and they wouldn't extend the companion fare to a new booking.

They did offer me stand by, and I do have MVP status (sadly only for this year) and yes it looks wide open now so we are likely okay.