If angels are like other cichlids I have worked with, they do fertilize after the eggs are lain. From what little I know of angels, I understand they are next to impossible to sex while alive, unless you witness spawning. Someone may coorrect me there though. I think the way to do it is to get a few, wait till you get a spawn, then remove all the ones that did not pair up. However, I didnt get a tank size so I dont know if this is feasable. Also, hatchets do better in schools, but this will depend on your tank size if you should do it or not.