I use the delta skymiles american express - I purchased 5 tickets (wife and kids) from the US to USVI, about a 2000 mile trip. My question is, should my wife have a separate skymiles account to get more Skymiles benefit. As it stands now, all purchases and trips are earn skymiles for me, however as I understand it, only the primary traveler gets credit for the actual miles flown. It's all very confusing.

Thanks!