What is the best lock for double doors in a single frame?
Sounds like you have “interior” french doors as opposed to them being on an exterior wall. If this is the case, the interior doors are typically 1-3/8″ thick instead of 1-3/4″ like the normal exterior door. The best thing to do is to measure the thickness of the door panel and call the local building supply house or locksmith shop and ask if they make a deadbolt for an interior door with the thickness of 1-3/8″. Then on the interior of the room put a lock at the top and bottom of the door, which is normally inactive, (not the one you always open first). This is a slide type that attaches to the door and then goes into the head jamb of the top and the bottom at the floor, they are normally called “flushbolts” and come in brass, chrome etc. Good luck.
