I smelt them and they didn't smell rotten. I tossed the two darker ones as I read elsewhere that they were rotten. I thought it was an outline of a duckling I could see and that's where I was getting confused!
The dad is khaki campbell and mum is a buff orpington, so I don't think they have special eggs.
you should candle them first. Looking inside can you you a lot about an egg. Especially if they don't smell rotten.