Originally Posted by WeekendTraveler

Having 2 seats in your name creates some risk that in case of a full flight or something, AA could cancel one of the seats; I've seen stories (although I'm not sure if they're AA-specific, and I don't have first-hand knowledge). And I would think that the gate agent could get really confused when you scan both boarding passes.

Also, on the manifest that the flighty attendant sees, I think that it lists the passenger's name, AAdvantage status, fare class (upgrade vs. paid) and maybe other things. I would confirm what the flight attendant can see and if none of the visible details would matter (for example, if you're John Smith IV and your parent is John Smith III or even James Smith, it wouldn't raise any red flags to the flight attendant), I would not necessarily mention anything.