I have done this a few years ago on United and it was fine. It might be worth a speculative phone call to ticketing to ask, or have a read of the T's and C's yourself to see what happens if for some reason one of you decided not to travel back on it. It does happen in the real world of course if someone gets sick and one has to travel back - but the airline industry has this thing about "hidden city" ticketing so can get funny about legs not being taken. But, I reckon you will be fine.