nelly27281;5141291; said:What should I do to make them fertile or this is the part of their parents job...?
The male has to fertilize them right as the female is laying them. Most angelfish today are so inbred and removed from the wild they don't know how to care for their young, and it's not uncommon that they are sterile.
If your goal is to breed angelfish, I would get some nice wild caught scalare, maybe a group of 6, and let them pair off. You should be able to sell the fry for some decent money too, since the parents are wild. A local supplier to me is selling 6 for $50 and they ship, so PM me if you want to go that route.