I did hear once of somebody who had turkey eggs in the refrigerator and gave some to a friend for eating. The friend set them in an incubator instead and if I recall had a pretty good hatch rate. If you look at mother nature, wild turkey hens start laying pretty early in the year and leave the nest until they have enough eggs, then start setting. If the size of the clutch is any indication, they have a pretty good hatch rate, too. So I think they can handle pretty cold temps as long as they don't actually freeze. If they freeze, they split open. Maybe try a few in the incubator with the chicken eggs or try starting them under a broody hen? If the eggs appear to be fertile, maybe it's the incubator? How long were they in there? Keep in mind that turkey eggs take 28 days vs the 21 for chickens and the shells are harder to see into, so it may take a little longer before you see development.