I think maybe you should take a picture of the light fixtures themselves. You said they don't have a sensor. More than likely they may not. Well that is what I thought when I put up an outside light once for a customer. They handed me the light, I took it out of a box that it did not come in. I wired it, put it up and the side of the house by the door, flipped the switch and it did not work. Wow, simple connections. I took the light off and put my meter to the wires, flipped the switch and got 120v. put the light back up and nothing. took the bulb out and put my contact tested up in the fixture socket and no power with switch on. Then all of a sudden it hit me. This is a wall sconce but my eye caught something. It had a small sensor at the top of the light which just looked like the nut to hold the two parts of the fixture together. Duh!!. I put electrical tape over the sensor, flipped the switch and the light went on. Here is something like what I am talking about. Notice the very small sensor at the top of the light.
HERE. Most people are used to looking for large sensors. These small sensors would be built in to the fixture and more than likely if one went bad it would not cause the other light not to work if that had a sensor also.
Also, upon looking at some of the pictures it is hard for me to tell what conductors go where. One thing I did happen to notice is that there are two sets of white bundles wire nutted and two bundles of black wires bundled with wire nuts. This may lead me to think that there are two separate circuits in this box.
Also the switch on the far right looks like a different type of switch than the other two. Maybe a pic of the back of all the switches may be helpful.
You say there is conduit and it may contain the conductors for the outside lights. If this is the case there may be a junction box somewhere.
