I can speak for Discus and say that they are egg layers. The softer the water, the better and lower the pH, the better of chances you have. Discus, depending on the experience of a breeding pair, will lay anywhere from a dozen or two up to possibly 150-200. The spawning process (female laying till male fertilizes) is about 1-1/2 to 2 hours.
After about 48 hours one of two things will happen. Either they will turn white and become hard, or you'll begin to see some coloration. At any point during this time, especially with new or young breeding pairs, they may be eaten by the parents. It's just their inexperience showing.
The fry will eat mucus from the parents slime coat for the first week and then should be moved to another (preferably bb) tank, at which time they should be fed bbs and then graduate to beef heart and other mixes. During this precious time period, they ABSOLUTELY NEED multiple daily power feedings and WC
's in order for them to grow out to beautiful specimens. A full grown, well cared for adult can easily reach 6.5"-7" and some quality show grades closer to 8".