High production layer breeds and the feeds developed in conjunction with them are the reason people say chickens stop laying at two years old. Most chickens do not stop at two, or even ten or more years. If your hens aren't laying now, it may be that they're all the same age so are all on their seasonal break at the moment, or they're undernourished.
If they're not high production breeds (this excludes the leghorns and possibly the americuanas and barred rock) then their meat may be fine even into old age but it depends on so many factors there's no guarantee. Even roosters can have tender flesh into old age, especially if they have bantam genes. But even if they're tough, they'll make good dog food or soup. Older bones hold more nutrition.
Or, if you can rehome them, they are at a great age to reliably pass on the best genetics they have. Younger birds simply don't do that in my experience. I've never got a breed-worthy chick from very young parents.
Kelp will start even non layers laying again. Hens from good genes and backgrounds can keep laying into their teenage years (in human years). High production breeds stop sooner. If you're so new to chickens you may want to hold onto them a while and learn from them. You're not emotionally or financially invested in them so can take a loss better than if you're spent money and time on them. but it's up to you. They will be immune to many things lurking in the soil around your place. I would still advise liming the ground to kill worm eggs and diseases.
I dare say you'd find someone who would want them, or several people, especially the blue egg layers. Your chickens are effectively in the prime of their breeding age now. Chickens can live for up to 20 or so years. We just don't let them, usually.
Best wishes.
