Unbeknown to us we had a double yolker in the incubator amd we did in fact hatch twins - but they didnt survive beyond a few minutes. At the time we were hatching hundreds of eggs so not just a few. I cant remember the breed ? Ixworth, White Sussex? Expect OH can remember. We were silly not to have taken a photograph to disprove the sceptics who dont believe it is possible. Never done it since though and wouldn't intentionally try to but you cant always tell from the size of the egg.