What size tank are the pairs in, what if any tankmates, and what do you have for decorations? Angels are usually not parent raisers, due to the breeding behind the various color morphs & fin configurations. I have 8 or 9 pairs, none of them are parent raisers, and none of the pairs I've had in the past were.
If they are eating them right after spawning, light the tank with room light only, and limit commotion around the tank. You can also try putting background material on the sides & part of the front of the tank.