Angels can take quite good care of their fry, and with a little practice they can have quite a good success rate. They do need to be alone in a ~20 gal
tank, as Brian says. Whether you remove them and hatch artificailly, or let nature take its course is probably a matter of doing more work vs. lower fry survival rate.
I left the parents in, and generally got a few fry survive to adulthood from each spawning. That was OK for me. I found watching the angels tend the eggs and fry to be fantastic to watch, although watching the attrition rate was a bit depressing.
Brian, what did you do to hatch the fry?