They're teens at 6 weeks. They may be laying and need extra calcium then, but they're not fully adult until 10-12 weeks. Kind of like a 13 year old human can get pregnant, but she's not an adult.
I answered your post in another thread, but it sounds like your temp was a bit high. It is a good idea to keep a calibrated thermometer or three inside the incubator because even good incubators lie.
I've been checking River Nutrition's web site, and it looks... scammy. There is no ingredient list to be found, it's full of claims for their Pure Cleanse that is supposed to get rid of parasites, but again, no ingredient list, no nutrition information. They're ringing all of my "Danger, Will...
It probably would. It would probably be easier to find eggshells that meet those requirements than oyster shells.
I really have my doubts about the nutrition of the Small Game Bird feed, though.
The pheasant breeder feed looks a little low in protein. lysine and methionine, but the small gamebird feed label is seriously lacking information. I suspect that it's because it doesn't contain great nutrition otherwise. Certainly not enough calcium for laying birds.