It's a good problem to have, but we do have too many competent backs right now so it's going to be impossible to keep them all happy without production suffering. Like someone mentioned above, at most, you want to split reps between 2 of them in competitive games because they need the carries to get into a rhythm.
If they all are almost interchangeable then the best way to keep them content is to play the older guys telling the younger guys they will get the mop-up duty while waiting their turn. The older guys should be better at pass protection too so there is that benefit. So basically it should probably be Scarlett and Perine getting most of the important carries with the other guys splitting the remainder. If Scarlett and Perine have big years they could move on to the NFL making Davis, Pierce, Lemons the "old" guys and the incoming freshman next in line.