I have used old feed bags for curtains. Chickens are quite inquisitive so they will investigate even though their nest boxes look different. Try adding curtains to two of them and leave the third open, so that if they don't figure it our they still have a normal looking box to use, but you may find they actually prefer the curtained ones. I would staple a feed bag to a pole or wooden lath and poke one end through the chain link just above the height of the nest boxes and fasten it however you can at the other end (not sure if you have chain link at the other side or how wide it is that you could put it through the chain link at both sides. Then use scissors to cut and trim as necessary. If you leave the curtains an inch or two short of the lip on the nest boxes, that is usually enough to encourage them to investigate and cut up the middle of course to allow them to push through them.
There is one thing for sure, the egg breakage is certainly not down to a lack of nesting material!! Those are very well padded nest boxes.
One question.....
Are the broken eggs in the nest box or out on the ground and (since I see you have multi coloured layers) is it only eggs of a particular colour being broken or is there no discrimination? Just wondering if it is a particular hens egg that it is happening to. Are the shells of the broken eggs good solid quality or a bit weak? I am doing my best to find an alternative reason for the egg breakage than blaming a hen for doing it deliberately, unless you have seen one break open an intact egg in front of you. What I find amazing is that the eggs that are broken are not eaten. None of my hens have ever deliberately broken an egg but I've seen weak shelled ones get accidentally broken or I've accidentally dropped and broken one and then it's a mad frenzy of egg eating to clean it up, so the egg lying broken but uneaten is really weird, be it hens or some other vermin that's breaking it.