I'll go through some generic stuff first.
I assume you are in Texas so north of the equator, plus some of them are molting. The most common reason for hens to stop laying this time of the year is the molt. You cannot always tell a hen is molting by looking at her. Some molt fast and look rough but others molt more slowly and it is just not obvious. At two and four years old I really think it is the molt.
Another common reason you think hens are not laying is that they are hiding a nest. As many as you have and assuming they were laying in the coop I would not expect this to be the sole solution, but it might explain a bit.
Another possible problem is that something is getting the eggs. Most critters will leave some evidence, either egg shells or wet spots in the nest. It's possible the hens can clean up some egg shells but usually not a lot of them. The critters that typically leave no trace are snakes, canines, or humans.
A snake will eat a few eggs, how many depends on its size, then stay away a few days to digest them before it comes back for more. I had a five feet black rat snake take four eggs at a time and visit every three days. If it is every egg every day it is not a snake.
If it were a fox or coyote I'd expect you to be missing chickens, not eggs. But sometimes a dog will eat eggs and not bother the chickens. Does a dog have access?
I'll leave you to think if it could be a human.
So what can you do? I'd lock them up in the coop/run for a couple of days. If you get eggs they are either hiding nests or you locked out an egg eater.
You can take an egg and mark it, then leave it down there. If it disappears them something is getting them.
That's all I can think of. Good luck!