chicks are life
Songster
X2 
Exactly what I was gonna say but you beat me to it!

Exactly what I was gonna say but you beat me to it!
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Those are Cornish Cross, specifically bred to be meat birds. Not long lived birds, even under the best of circumstances. One group is at about slaughter age of 8 to 10 weeks. The other group, with larger combs are look like they are about laying age.
All Cornish Cross, just different ages. The bigger combed birds are simply older. Those should have been processed months ago.Are they both Cornish cross or is the ones with a bigger comb different? Some of them are laying just don't know which ones.
How many of these birds do you have?
In the pic notice how all the older ones are laying down and the other chicken breeds are not.
Its because Cornish are bred for meat so they get to heavy to stand so they just lay around all day except to eat,drink and lay.
I would increase exersize like free ranging.
I would consider culling the older ones if you arnt attached so they don't suffer.
They are prone to joint/mobility issues that make getting around difficult. They also have heart related issues due to their massive size. Even if carefully managed to control their growth rate while young, they rarely live longer than 6 months of age. The truth is, they aren't going to live happy, healthy lives. Their purpose in this world is to end up on the dinner table.We just bought some from an auction not knowing what they were. I do let them free range part of the day.
How long do they live? Thank you for your help.