When they start laying does depend some on breed but it is also a very individual thing. Not knowing the breeds, I also would expect you to be getting more eggs, but sometimes that just doesn't happen. Just bad luck. But what I would really look for in your case with them at that age is are they laying and you are not getting the eggs. I'd really be suspicious that some are hiding the eggs from you. I don't know how you are managing them, but if they have a lot of territory they could be hiding a nest, I'd try locking them all up for a couple of days to see if your egg production dramatically increases.
If you were getting a wide range of number of eggs each day or they had a variety of appearances, I'd think of something eating some of them. But since yours appear to be regular, my thoughts are more to them hiding eggs from you. Don't totally ignore the possibility that a pet dog or something is eating some eggs, but with it being this regular, I kind of doubt that is your problem. By the way, that Rainbow Mix does not mean a variery of egg colors. It means a variety of colors of feathers on the hens.
As far as them scratching the nesting material out, try putting a larger lip across the bottom of the nest. I had to go wtih 5" to 6" lips to stop mine form scratching the nesting material out.
Don't get hung up on that laying cycle. It normally takes about 25 hours from the time an egg starts its journey through the hen's internal laying factory until it is laid. There is not necessarily a connection to when the first egg is laid and the second egg starts its journey. I've had hens that lay regular as clockwork the same time each day, which means the second egg started before the first egg was laid. It is also not that unusual for a hen to lay two eggs in the same day, usually a pullet first learning to lay, but sometimes a mature hen will do that. That means the second egg started its journey a long time before the first egg was laid. When she does, the second egg is often soft-shelled because the shell gland has not had enough time to make enough shell material for the second egg. There is not a lot that is consistent about chickens.