Back in September 2014 I booked 2 reward seats in First to Chicago for August 2015. At the time I remember there being 2 CW seats also available on the same plane. And this level of availability was across numerous flights. I didn't have enough avious though, so had to pay cash for - like you - the remaining members of a family of 5, and split the booking.

I think it was just pot luck though, and like you expect the number of reward seats to be close to the bare minimum in most cases for long haul. I've been doing a fair amount of searches of late for February 2016 half term, and apart from a small number of exceptions, there seems to be a max of 2 CW reward seats per flight.

Gary.