Yes - it is inconvenient and they will have to climb over people if the seats are in sleeping position. We preferred B and D - sitting across the aisle from each other, both facing forward and both on the aisle. As an alternative, you can try upper deck - at least they will be climbing over each other but the seats are 2-2 so it is less crowded.

The first feeling you get in the lower CW cabin is, "Wow! Could they squeeze any more people in here!" If it were my grandparents, I would pay extra to reserve seats so they would have the most comfortable experience.