as long as you keep them clean, fed and give them clean water. Also avoid all possilble sources of stress, in other words keep them happy.
Lime is cheap and will kill a lot of parasites and makes the bird less attractive to redmite. It is one of the best tools in my kit.
All the illnesses i mention are very complex, and can devestate a commericial flock. For a few hens it shouldn't be a problem.
I'm sure you will be fine.