I have a broody khaki campbell duck and she has been sitting on her eggs for 20 days, i caught her out for the first time today so went to look at the eggs, candled 3 out of 20 and the had a big air sac and dark shadow the rest, does this mean they are infirtile and if so what are the cances all the rest are. I have 1 drake. Should i be worried or not? will any hatch?