Before you get ahead of yourselves you and your DH should know you won't be allowed to sit next to each other UNLESS you get that 3rd seat. Since the babies are so young you could sit them on your lap, but due to O2 mask placement you wouldn't have enough in one row. If you get that 3rd seat you should be ok. Next, I would request bulkhead seating if possible. It will give you more room for your gear and to move about. As for diaper changes, I don't have any good recommendation for you. We didn't fly that far so we were able to do changes at the airports. Flying with DD at that age wasn't horrible, just pack lots of snacks, and put some surprises into the bag, like new toys or books. HTH.