The "trick" to keeping multiple Angels in a tank is more about the decor and which ones go in when. Since most dwarf Angels are hiders, they need a lot of cover in the tank to make them feel secure. If there is not enough rock work or "cubby" holes, the fish in there first will knock out anyone that comes in later. So one person can have much success with the same 2 Angel types that someone else is having a disaster with. So the best way I have found to keep multiple angels is when adding a new one, add another piece of decoration as well.
Hope this helps