I agree with the others. It would probably be best to leave them be.
Bringing a more suitable bed nearby is a great idea, hopefully she decides to move them.

I do have to say that I personally think you should peek in on them IF momma cat does not mind or you can keep her occupied or closed in a seperate room just for a minute.
Don't disturb them JUST LOOK to make sure they are all alive & appear healthy.

Congrats