If both lights are controlled by the same switch, turning the switch off should shut down power to both photo cells and lights.
Those units are minatures and are not made for more than 1 bulb.
Probably why they burnt out quicker than normal.
They will not control 2 bulbs or 2 fixtures.
There are small wattage cells.
In order to control both lights off of one photo cell, you will have to find where the wires from the lights go and connect on the other end.
With one white at each location, your lights are not wired between each other but meet at the switch or a junction box
If they were connected directly to each other, you would have 2 whites at that first fixture and not one.
As for the type, if you are controlling 2 fixtures, you will need the large photo cells, as they are the only ones to carry that type of wattage.
Higher wattage cells have 3 wires.
Those mini button style are made for like 60 watts maximum and they dont make the smaller ones to control large flood lights.
Larger ones like below are made for the higher wattage.