I feel sorry for you and your chickens, this is very unfortunate! If it was wry neck, wouldn't they still be able to walk though? My experience with meat birds is very limited, but I do know that when birds of this breed get older and bigger some of them just can't cope with their own metabolisms... My friends usually raise 100 of them every year, free ranging too and organic feed, and once some of them were starting to collapse and die of a heart-attack it seemed like, so they had to make the butchering happen faster than predicted... Sorry, I am afraid I don't have a solution for you! Maybe someone else will be able to give you a different perspective... and it would help to have a picture... Don't give up on them!