Hey, Buffy,
It all looks complicated to me, too. I know what to do for my dog or cat -- I take a poo sample to the vet and he checks for worms, and then, if they have worms, we decide what kind of wormer to give them depending on what kind of worms they have.
I'm thinking you could do the same thing for your girls.
But you're right that if they look healthy you probably don't need to worry too much. In the old days that was called "the eye of the master." Pick them up now and again. If they feel heavier than they look then they're just fine.
I'd be curious about the tail feathers, though. Again, pick one of them up and look through the feathers for bugs.
maggie