You could do JER-LGW-NYC in Club World for 200k Avios + £983 for two people in Oct-19. You'd need to get to JER from LPL or MAN for your outbound so that depends on you and your wife-to-be's desire for a pit-stop in JER.
The easy life is a direct economy flight from MAN-NYC for around £350 each on a cash booking and use the Avios for a nice hotel, as suggested above.