Two roos for each 4 hens? That also doesn't sound right to me. I have 20 hens and 2 roos, so 1 roo per each 10 hens. The roosters will beat the hens up if he doesn't have enough of them.
Most websites recommend 1 roo per 10 hens. When I had too many roosters, the hens were mated with...
Since the Cochin seems to have dominance over the silkie, I would leave them to sort it out.
I have this kind of problem, except they didn't work it out so I have to separate one of them.