If all of all of your other birds are pure breeds and it just happens occasionally then they may be laying twice in a day. (it is pretty rare in chickens though) My quail however, I'm finding will do it fairly often. They both laid at 10:00 last night and around 11:00am I found a nearly shell...
It is extremely rare to get two eggs, I have had it happen twice so far and both times one was laid at approx. 6:00am and the other close to 10:00pm. I would suspect that you have two more EE's that look different. That's the thing about mixing breeds, as they are not one specific breed, they...