I'd leave them alone. If you have a cardboard box around, you can make them a 'huddle' box. Basically, you just cut out an opening so they can get in and out, and it helps them feel more secure, plus retain a bit more body heat while they feather in. Removing them from the flock would just mean reintegration stress later on. At 4 weeks they do generate quite a lot of body heat, and huddling together they way they are is likely keeping them all plenty warm. Chicks are much more hardy than many think.
Thank you! They are in an enclosed box where the mama was sitting as a nest (it's a plastic dog/cat crate). I wasn't clear before though, they are in a separate pen from the rest of the flock. I have many different barn sections for chicks, breeding projects, etc. So when she went broody she got her own apartment. I was actually wanting to move her nest box into the main flock soon.. do you think she'll continue to care for and protect them during the day now that she's roosting?