Pine shavings are fine in a nesting box. I've used pine shavings, straw, and hay, sometimes alone and sometimes combined. They all work. I don't know what the shavings you are talking about are made from though. If they really are pine, they are OK.
It won't hurt for them to eat some shavings. If they are out foraging, they will eat bits of wood and all kinds of things. As long as they have grit, they will grind it up in their gizzards. With anything, it is possible they could get an impacted crop and anything includes shavings, but that happens so rarely its not even on my radar. Don't sweat it.
The fumes off cedar shavings can cause problems to a chick's respiratory system. A lot of people seem to have problems understanding that can does not mean absolutely, every time, without a shadow of a doubt will, but it means it is possible that it can happen. Whether it causes a problem or not is going to depend on ventilation, how fresh the shavings are, how fine they are shaved, and many other things. But yes it is very possible cedar shavings can harm your chicks. I don't use cedar. Pine or Aspen shavings are not a problem though.
Cedar lumber in building is not a problem either. Shavings have a lot of surface area to give off the fumes. Lumber does not have nearly as much surface area. If you build a coop out of cedar and provide the ventilation they need, you will not have a respiratory problem and cedar lumber lasts a long time. It is kind of expensive though.
