It's rare but it has happened. It's best not to try though because you can end up with really messed up chicks out of the deal and there's no need to put little baby birds through that.
yes it is possible but very slim chances usually they die right before hatch. if they do make it they live a very short life and usually have like 3 or 4 legs or double headed ect. or the extra limbs die off, it depends how the 2nd twin is attached and what connects them.
there is even with room usually not enough room for them in egg so they either die in shell or are born as conjoined siamese twins, i think that's what they r called. i've never heard of a set of actual identical twins hatching from them from 2 complete sets of yolk/white within not attched together. it's always been conjoined somehow like it is with people but there maybe cases of it i just haven't heard. if u look at the ripleye's believe it or not site online u can see some with 4 legs ect.
Conjoined would be if one embryo split into two and they didn't fully seperate. Since it's two seperate yolks, they shouldn't combine into one embryo. I think someone on here may have hatched a double yolker and had the chicks survive.
I'm on day 18 for my twins.they are both same size inside and the egg is enormous and shaped perfectly :/ I truly hope they make it to full hatch. I've been very careful and very adamant on checking/candling. They are both moving and look "normal" ? I will keep you posted