Most Corydoras won't breed until they are mature at 2 years old. Some breed at a year but most take longer. You need to feed them well (3-5 times a day) and do big regular water changes and gravel clean the substrate.
You can encourage them to breed by lowering or raising the temperature a few degrees overnight. Most breeders will use cold water (5-10C cooler than the tank water) for water changes, and do a 50-75% water change each day for a week. This simulates rainfall and usually gets them breeding.
If the guppies are well fed they usually ignore the eggs and babies but there is no guarantee, especially with eggs that are stuck on the glass saying free food. If you have lots of plants in the tank and maybe some leaves on the bottom, the babies will have plenty of places to hide. Personally I prefer to breed fish in single species tank so there are no other fishes in the tank to interrupt breeding or eat the eggs/ fry.