If planted too deep, they will use all that energy just trying to reach the surface. If they don't get there, they can't manufacture their own food. The stored energy is gone. It should be moist, not swampy. The fluctuating temperatures you mentioned could be the problem.
Seeds generally germinate better and faster with consistent bottom heat .
70 to 85 degrees Fahrenheit works for most seeds. Seeds sitting in wet cold potting mix will usually rot rather than sprout. Be sure to get the book I mention below for your wife. It's the best one available for hobby greenhouse gardeners. Here is the contact information for my favorite mail order greenhouse supply business.