Ddawn hit it.  You have two different issues here.  
Oyster shell provides calcium.  Layer is formulated to have enough calcium so that you do not need to add any more calcium if layer is all they are eating.  If they are eating other things that provide calcium, like dairy products, hard shelled bigs, certain green plants, rocks for grit in limestone country, such as that, they are probably getting plenty of calcium.  If they are eating things other than layer that do not provide extra calcium, they may need a calcium supplement.  I go by my egg shells.  If the egg shells are hard, they are getting enough calcium.  If the egg shells are soft or thin, they need more.
Normal layer for chickens contains 16% protein.  I wonder if that 22% layer is meant for game birds, not chickens?  If 16% layer is all chickens eat, that provides them enough protein and other stuff they need to lay efficiently.  If they eat a bunch of stuff low in protein, then an additional protein source is a good idea.  If you are feeding a feed that is higher than 16% protein, I'd suggest you feed them other stuff low in protein to kind of balance it out.  If they are getting too much protein, their internal organs (not sure if it is the Kidneys or liver) has to filter it out of their system.  Scratch is a good example of something lower in protein, but I don't like to feed much scratch due to the high energy content.  Too much scratch can make them fat which leads to other health problems.  
Don't get too stressed out by what I've said.  The margin of error is pretty big on this.  These are not targets you have to hit exactly, just general targets to aim for.  Chickens are pretty tough and adaptable.