When my birds were laying double yolkers, I did copious amounts of research to find reasons why (no good answer no matter how much you look, nobody has considered it study worthy. basically, it's hormone-related, a bit like when a teenage human starts out with an irregular period, before it settles into routine) and how it might effect them. I also found out that it is extremely rare for a double yolked egg to be successfully hatched. Almost always, one or both chicks die. I have found nothing regarding hatched chicks surviving to adulthood, but I would think it wouldn't come without its problems. Probably best to toss it. Not worth the novelty, in my opinion. But how dedicated are you? Are you prepared for the possibility of life-long vet bills for a deformed chicken? I'm not. If I was, I'd adopt one, not make one. I'd really think about it.
