My suggestion is to configure nighthawk as an AP only (no dhcp). Then, setup the pi with a static ip.
public ip -- nighthawk -- 172.16.0.1
172.16.0.2 red --pi-- green 192.168.1.x
pi will provide dhcp/dns to clients
you could have an alternate setup:
modem -- (red) pi (green) -- nighhawk (as AP 192.168.1.5 offering wifi)
keep 192.168.1.1-9 as static (AP, printers, nas)
dhcp green 192.168.1.10-250 all clients (wired, wireless)