x2 on the clutter inside the run, helps keep birds busy and provides hiding spots.  Piles of green materials - dried leaves, pulled weeds - also will provide some entertainment so they can focus on something other than pulling feathers.
I'd also see about switching to an unmedicated (feed without amprolium) chick starter or grower feed, as those should have higher protein %.  Aim for 18-20% protein.  You already are providing calcium via oyster shell so layer isn't necessary, though since you already have the feed you can also consider feeding a mix of half layer, half 20% protein feed (that'll balance out to 18%).