When I began reading your thread this was the exact things that made me feel you were some sort of chicken saints. Not going there everyday, or bringing them food, or spending three hours on the bus back and forth, or dealing with C. (Although all of this is certainly to your credit I think you made it clear that was it something you wanted and that being with chickens was a daily task that gave your day sense and structure.)
Having to deal with the fact that with all you do for them, you will see quite a few of them through their last days and death, that will necessarily come on a regular basis due to their age... that's something I find really admirable. I hope you can find some way to deal emotionally with it, I wouldn't be able to.
This and Rib's words lift a heavy weight for me! I've never had to cull a chicken yet. When Vanille was sick we kept wondering what we should do, not having experience, or a vet's advice. We did hesitate to cull her but then she healed completely and has had another six months with a very good quality of life, up to now.
I think I would be way more serene to know that if it feels like a hen is very near to certain death I will leave her with her tribe, and only cull if death does not come naturally after a given number of days. Pain medication changes the deal.