Yes, you were probably already thinking these things yourself. It's always helpful to hear from someone else who has done it. That's what makes BYC such a success! Members helping and encouraging each other!
I would suggest giving them some outside time each day, extending the time each day, and making very sure they don't get any breezes on them! They need to build up their feather coat and this will help.
The other option is putting them out with a heat lamp starting at 70 degrees and dropping...