Mr. Travel_addict and I always book our tickets separately after we tried to book 2 tickets together once and found that the tickets were $40 more than if we booked separately. Yes, it's more work and there is a chance of inventory selling out but sometimes it has worked in our favor: co.com will list "Only 1 ticket available at this fare" but we will both get it. The one time he booked first and it was gone for me, another ticket in that fare bucket got released a short while later.