Please try to figure out what the problem is. Killing them is not a solution. Your next flock will probably have the same issues if the circumstances are still the same. I have 8 and 9 year old heritage breed bantams. They take a long break in winter and are broody sometimes. But otherwise they still lay about an egg every other day.
I agree that it is best to try to figure out if there is a problem so you don't repeat it in the future. But I must admit that I started off with meat chickens that I harvested at 10 weeks. So, replacing non-productive laying hens is not an issue for me. I also plan on replacing my flock every 2 years because it costs a lot more to carry them over the winter if they don't lay eggs. I also don't consider my flock as pets and, on purpose, don't get too attached to them like you might with a family pet dog. But that's just my way of keeping a flock. I appreciate others who feel differently.
I just hope that OP does not feel bad if they decided to replace the current flock and try some new breeds, for example. Some of us do that every other year as our plan.