If you put a seperate dish of Oyster shells out for them they will take what they need. It shouldn't affect the hen that is laying the hard shells in a bad way.
There is a product called poultry Cal which replaces the oyster shell and grit so you don't have to have two dishes out, just one.
While you are looking at their vent take a close look at the feathers and skin above the vent. Spread the feathers apart and just watch. Look for any critters crawling around. Lice move quick and are flesh/light brown color. Norther fowl mites are tiny tiny little critters the size of a pin head or smaller. If they have mites you will see that their feathers around the vent look like they have poop stuck on them but it is actually the mites and their eggs.
I'm not saying that they have either of these but as long as you are looking at the vent it is a good time to check for bugs.
Also if they have a bad case of mites there may appear to have scabs around the vent whole.
I have silkies and they are notorious for getting Norther Fowl Mites. This is the time of year they thrive.
Kristip..... as for trying to get your pup to quit biting hands and fingers. I've done this with my dogs and it works too. (Wouldn't let younger children do this however) When the pup takes you hand or fingers into it's mouth stick you finger as far back into the back of his mouth, like gag me with a spoon effect. You want to make him want to gag, Do it quickly and say NO BITE while you do it. The kids can say NO BITE in a stern voice once the pup knows what it means and it may help (or may not lol) depending on if the pup respects them as alpha yet.
Ok, that's it for now.... Waiting for the septic guy to come. TO you started something. Sure hope it isn't a constant thing this winter for all of us. Our septic is backed up. DH thinks it's because I flushed the chick waterer's with chips in it down the drain and toilet for well, let's just say months......
All he said was GD chickens !!!! Glad I wasn't the one who wanted chickens to begin with.