What kind of nest setup are you using? Is there any bedding in the nestbox? Do you provide extra calcium or any other supplements to your breeding pairs? What kind of diet are they offered?
First step would be to figure out why the eggs are breaking so that problem can be fixed. My first thought is the eggs might have cracked because the shells are too thin - this is usually caused by lack of vitamin D or calcium in the diet. Or they cracked because the nesting location is inappropriate, so the female is breaking them by accident when moving in and out. A picture or description might help identify potential problems, like a box that is too deep or wrong bedding choice.
Personally, I would discard the cracked egg ... BUT it is possible for a slightly cracked egg to hatch successfully. If you want to try, you will need to seal the crack. With chicken eggs, the recommended strategy is to seal all cracks using wax from a candle - you want to select a plain unscented candle made from pure beeswax. Drip the hot wax over the crack. Do not cover the entire egg in wax. The egg needs to able to "breath" through the intact shell. Do not wash the egg, as this will remove the protective bloom that keeps bacteria out of an unbroken egg. Handle this egg with extra care to avoid further damage and discard it if it fails to develop after a week or two. Rotten eggs can explode, if they are left out too long.
You can move eggs between nesting hens, if the timing is close. They generally don't question where the new egg(s) came from and treat them the same as their own eggs. You could move the uncracked egg over, if you want. Just be aware that if the shell is too thin, it might still crack in the new nest so keep a close eye on the egg. If the eggs are similar size/color, mark the sun egg with a pencil so you can tell which one after it gets moved around.
