Can you identify who the 2 who laid the eggs inside the coop? There would of been shells in the carnage so if you didn't see any, there probably wasn't any. Shell less eggs are not uncommon in new layers. Chickens live to peck at things so the egg was new and interesting so curiosity got to them and now the cat is out of the bag. They know where the good stuff comes from. Bored chickens find trouble. Treats thoughout the day will help but too many will bring down the protein and Ca level of the layer feed to the point where you really need to add some back. I feed back egg shells for Ca but because they are eating eggs, I wouldn't do it unless you crush them or hide them in another treat. That's where oyster shells or limestone comes in to play. You can sprinkle out feed and oystershells as a scratch so they have to work harder and longer to get their food (what else do they have to do?) If it's hot, freeze them some ice blocks with treats inside (vegetables, stale bread, cereal, pasta, cheese...)
Eggs need to come out rock hard. If they're too soft, they will crack just in the laying process. Also make sure your nesting boxes are in the quiet and dark area of your coop. If the problem persists, there are nesting boxes that are built at a slant and the egg rolls away and get trapped out of the hens reach. You can probably find plans for them in the coop section.