I tried mixing a group of Speckled Sussex that were going on three weeks old with my one-week old Buff Orpingtons and it did not go well. I got the advice from this site to put up a chicken wire divider in the brooder and since then they've been happy as clams, so I think your idea of starting out by dividing the rabbit hutch is a good one. I guess how they get along depends a lot of the individual breeds (or maybe even the individual chicks). I tried taking down my divider after about 4 days because the little Orps were trying to get through to the other side but once the divider was gone the Sussex scared the daylights out of the Orps again - so I put it back up. I'm going to wait until the Orps are more the same size as the Sussex before taking the divider down again. Since your groups are both Silkies the introductions may go a lot more smoothly.