I posted a thread about my Silkies a few weeks ago, because they were so different from my other chicks and I wondered if something was wrong. Mine just stood in one spot all day too, though would go eat and drink on their own. They were half the size of the d'Uccles, who are only a week older, and very slow to feather. They are now seven weeks old and much livelier, though still not as feisty as the other chicks. Howver, they are in with eleven ther chicks (mostly standards) and can hold their own now. I've also caught them going up and down the ramp in our run which apparently a lot of Silkies won't do.
hopefully yours is the same. I considered separating mine because I wanted to put he rest outside, but for reasons Chickensaresweet said, I didn't. They are the smallest and youngest and I'm already worried about integrating them with my other group of chicks. Having to reintegrate the Silkies with no other chicks to protect them would be a nightmare!