RosemaryDuck
Crowing
So, just wanted to add: Since you already know it's very rare if it hatches, just know you'll likely have to start a pip for the twin on the other side of the egg. Usually when twins form they face away from each other in the egg and one will not have access to the air cell. So once the first one starts pipping, the other will have no way to get access to air. So just keep that in mind if they do make it to the hatch date. One will also hatch much, much smaller and likely weaker since usually 1 takes most of the nutrition.