Having watched plenty of chicks hatch out of their eggs, I would think two chicks sharing an egg would have to be pretty small as I don't think they'd be any room left in there.
Now I want chickens again.
I love chickens. My riding instructor/trainer has a buncha chickens. Her rooster keeps sizing me up tho. I often have to chase him around when he tries to chase me. Interesting that I can be afraid of a tiny rooster yet I can push around a draft horse whenever they're not respecting my bubble.
I love horses and chickens. Years ago, a man had chickens across the street and a lone chick made it over to our house. It had to have been only a week or two old, and he sat at out doorway for hours chirping. So we took him back to the man and two years later the same chicken, now grown up, came back to our house and lived in the treehouse.
It was so cute and I loved spending time with it. I also loved the free eggs, too ;)
Haha we had this rooster called Brutus that my mum used to have in her bed in a sock when we first brought him home after he was abandoned by his mother.
He was the most aggressive rooster ever. He would fly at our neighbour's face (he had her completely bluffed) and would spur your legs and feet if you turned your back on him.
He actually gave me cellulitis after he spurred my foot and I neglected to wash it and several hours later it turned swollen and red and it was off to the doctor's clinic.
Of course he was maybe the size of a soccer ball (he was a bantam) and much to his disgust I would pick him up by the tail and carry him around under my arm to stop him being a nuisance.
When they are bigger it is a lot more worrying as they can be quite savage. I don't generally advocate using physical force but in the case of roosters sometimes the only thing that gets through to them is a well-placed punt.