Try paper towels on top the shavings. That will keep down any dust or odors from the shavings and will make it easier for the chicks to get around. I've been using a double thickness of paper towels on top of shavings and it works well for my chicks. I also agree about checking on the heat as I...
I'm sorry I don't have any advice. I've only had chicks for the past week myself. I don't think the change to pine shavings would kill two of them in that short a period of time, especially since one had died previously and two arrived dead. Have you tried any electrolyte solution aka Sav A Chik...