There are different opinions on how you need to treat the egg shells. Some people wash them, bake them, and/or crush them. Some of us just toss the halves where they can get to them and never get egg eaters. Just be comfort with how you want to do them.
The hens seem to know when they need extra calcium and when they don’t. There are a lot of different ways they can get calcium, feed, oyster shells, egg shells, some plants they eat, some creepy crawlies, even some gravel they use for grit if it is limestone. You can offer the egg shells on the side. They might eat them, they might not. It won’t hurt to give them that choice. They might prefer oyster shells, they might prefer egg shells, they might eat neither or both. If their egg shells are hard they are getting enough calcium, that’s what is important.