If you and your husband don't have any elite status with BA/oneworld you will indeed be one of the last groups to board. Depending on how early you get to your seating area will determine whether you will be able to put your luggage above you or whether it will have to be a few rows in front or behind. However, on big widebody planes like this will be, there will almost certainly be space somewhere on board for your luggage. It is very unlikely that it will have to be checked at the gate.