Normally one dies in shell and the bacteria kills the other. They are not viable. I read one person actually had a chick hatch but it somehow absorbed the other chick and died.
I’ve heard it’s possible, but very difficult to hatch doubles. I was following one thread for a while where someone was trying to hatch double yolkers, if they started developing both embryos would die pretty early.
More pullets are starting to lay. Right now I know both EEs are laying, both Orpingtons, and both Brahmas. I have 2 SLWs that should be but I haven’t caught them in the act. My 2 youngest (Dominiques) I don’t think so. I don’t know exactly how old they are. They were a bonus with Rusty the Rooster. I think my 5 remaining big girls are all laying, just not every day yet. Egg days are looking up! Go chickens!!!
I’ve heard of several people on here that have tried to hatch them. Most just die. I think I remember 1 person that successfully got both embryos to hatch but I don’t remember who it was.
