I just did exactly what you are trying to do for a RT flight to Brussels with Delta and an AF codeshare. 100k UR points for 2 RT tickets on AF and 1 RT ticket for a Delta Skymiles award. My wife, son and I were all able to sit together for all legs (seats were available). I tweeted Delta to link the PNR's as single passengers have a tendency to be moved to accommodate larger groups. A couple of notes: We flew from DEN and I would suggest that the flights through JFK as opposed to ATL are preferable as they are like 2 hours shorter for the TATL leg. I also traveled in Y and couldn't have had a better experience. Great service and attitude on every aspect of the trips, including an easy reroute on one leg due to an IRROP- Thanks DELTA! Don't forget to use the lounges since you apparently have the CSR card. I found that some of the lounges give you access on the day you arrive without requiring a same day outbound BP-YMMV. Happy flying! PS make sure you go to the gate for passport validation... Hope this helps!