Wow. That would be nice to have two dwarf angels in a tank. What size tank do you have skennelly?
Typically they'll attack each other until one perishes
'course once territories are disputed things might settle down - if this is the case then the only suggested way of doing this is adding both at the same time.
I, personally, wouldn't suggest it. Especially in a 55g.
With your current setup I would get the coral beauty as it tends to stay smaller than a bi-color and would go well with your yellow tang and clown.