How months old are they already? because you can only certainly know that they are rooster if when they reach 5months old. Roosters at that age have distinctively glossy, angular saddle and hackle feathers.
If your chicken likes Oyster shells, then good for you. Know that oyster shells are necessary for chickens because they supply 20 times more calcium to their eggs than their bones do. But in case they don't like it, I found a product that has calcium too that you can give to your chicken. I...
Treats are good for chicken, especially when these treats are healthy and your chicken loves them. Just make sure, you give them enough treats for a day, because I'm a firm believer that too much is not good anymore.