I would try using the smudge tool or the Liquify tool to create a softer look for the feather. Just drag either tool from inside the feather to out, and experiment with the direction you drag. It will create soft edges that gradually taper off. FYI- To get the best results, you'll probably have to remove the outlines from your feathers. Which might mean removing the outlines from all of the elements in your scene, just to keep it unified.