Well, I don't know how far along either of the eggs are. I had to remove them from the box because we already have 9 chicks that two of the hens are mothering. They choose the box with eggs in it over the one that didn't. I lost a chick the other night because they were unknowingly incubating the eggs in that nest. It was newly hatched and the hens crushed it. They've been sleeping in that box for about 4 days at most. I've had the eggs in the incubator since last night. When I candled the eggs I wasn't paying much attention to their size, I notice THAT today, and I noticed that on seemed to have a very big chick in it. I did it again before I posted and I noticed that the movement doesn't happen at the same time, rather one spot moves and a few seconds later the other one moves. Both 'dark spots' have been moving quite a bit and in the other egg the chick doesn't move near as much. I would post a video of it moving, but my camera doesn't pic up on the light inside the egg.
Not only would this be my first fertile double, this would be my hens' first double ever. It's never happened before.