To answer your question about carry-on, if you let one of the agents who is managing the lines know that you don't have checked luggage, they will let you go through ahead of those who do. In your case, splitting up certainly makes sense to me. We generally travel with carry-on only, but for the past three years have checked a small bag with liquids and consumables. We don't check a bag on the trip home, which makes the connection in the US easier.