@hennybee , an egg eater can be a chicken , or maybe a rat or a snake?
Are you sure its a chicken who eats the eggs? Camera?
To get a better idea of the we need to know what breed(s) you have and how the live. Most breeds with 2yo chickens should lay more eggs than a few each week as you say. So maybe it is a food thing way from the start.

But it can be something else too.
Where do you live? Whats the temp?
What do you feed them? How much protein, calcium , other ingredients? Did you ever try another brand?
Could it be stress related that they don’t lay much?
How big is their coop and run? Do they have access to herbs and grasses? a compost pile? Sun and shade? A sandbath? Did you ever check on parasites?
It might help if you can let them free range 1-2 hours before roost time. Supervised if the predator is very high where you live.