Yes, your dad is right to some extent. Egg shells is a good sorce of calcium though for your chickens. This is what I have done by the advice of other, more experianced members.
I take all my egg shells and put them in the micorwave for about 15 second to kill anything that may be harmful to the chickens. Then I crush them up fine so that they no longer resemble an egg. Then feed to them.. BUT, do not use this as your only sourse... you also will want to provide them with oyster shells.
You can also put them in the oven on 250 if you do not have a microwave for a few minutes.
I have been doing this for weeks, I have not had a single chicken peck at my eggs or eat them so far. You can also put golf balls in the nest... they not only teach the hens where you want them to lay, but also it acts as a deterant for pecking... it has a bounce back effect.
You NEVER want to feed your chickens Chocolate or Milk. However they can have a certain type of yougart.
They do love any type of mellon and tomatos and I know mine love macoroni salad lol.
Good Luck.... Tes