I will look into that.Here is an article on trimming nails and spurs. Perhaps you can trim his down to the point they don't cut up the hens.
I believe I would first separate him for a while to give the hens a chance to heal. Perhaps you can find, make or alter their saddles so that their sides are also protected. Also, it may take some time to get his nails and spurs down to an acceptable size, and you can only take so much off at a time.
I would cull the rooster.