It is not uncommon for angelfish to spawn in a group. It usually happens when there isn't enough space in the tank for the number of fish it holds so that a pair can successfully defend a territory. The problem is that literally every time they spawn in a group, they also eat the eggs almost as fast as they lay them. So, what seems like it might have been a good thing, is actually a sign that the pairs need to be separated and given their own tank.
In this video, there are 6 fish participating in the spawning and a few fish that are not allowed to. (sorry for the video quality, but it was a very dark tank, with mostly darker colored Orange Marbles in it). I don't often have a camera on me when this happens, so I grabbed this short video even though conditions weren't ideal for viewing. Hopefully you can see it well enough to make out what was happening. As usual, the eggs were eaten as fast as they laid them.
Here's another video I took awhile back:
Once we move a couple of pairs out of this tank, the remaining fish are not likely to group spawn again. As always, comments are welcome.