We get asked this question a lot. French doors come in a variety of configurations. One of the most common ways they are built for interior applications is to have one side of the door fixed and the other operable. Then if you want both doors open you can unlock the center style using the latch located at the top of the fixed door (unfortunately we don't carry those latches in different finishes at this time). If you have one door that is fixed and one operable, chances are the operable door has a hole bored for a Door Knob or lever handle, while the fixed door does not. In this case you would want to order a knob set for the operable side and a couple of dummy knobs or levers for the other side.
If both doors have holes bored in them, you will need to order a knob set for both doors and leave the latch mechanism out of the fixed side. A dummy knob will not work on a door that already has a hole bored in it. Dummy trim knobs and levers are face mounted with screws to the surface. If the door already has a hole bored in it, there will be nothing to attach the screws to.
Exterior Double Doors. The above will also apply. If you need dummy handle sets for a double set of entry doors we have them available for the non-operable side of the door.