Queen excluders will allow the bees through, which means they will make one cluster around one queen and abandon the other queen. i would not recommend it. Worse, they may cluster around the bottom queen at the start of winter, leaving the one in the top to die of cold and then work their way up to the top by the end of winter leaving the other at the bottom to die of cold. The cluster will follow food, not queens. This is not a good plan. If you want to combine, then combine with no excluder. If you don't want to combine, do not put excluders between. Also do not put double screens between because they will allow all the moisture to move to the top hive which may not be able to handle the moisture. If you want to stack them, just stack them or put an inner cover between with the hole blocked with duct tape on both sides and staples to make sure it stays.