Your doing the right thing with the bbs. IMO if you can't take the time to hatch bbs for your fry, then you should just let nature take it's course. Egg yolk and crushed flake might work for livebearers, and you may end up with a few angle fry with this method, but if your going through the trouble to maintain a seperate tank and actually raise fish, then do it right. Live bbs twice a day. 50% WCs twice a week. (you can do both of these more often if you wnat to )
Look to remove the babies after they've been free swimming for 1-2 weeks. After that they become difficult to siphon out becuase they stay too spread out at night. Good Luck
BTW if the parents don't eat them, I would make the fact that they were "parent raised" a selling point. Too many angels these days are artificially hatched and raised.