When you first introduce the new angels into the tank, of course, they will hide for maybe a day or two... After that, they'll realize that there are other Angels in the tank... Now if the two original angels are mating... that's the only time I would imagine some fighting... Don't get too worried about it though.
I think that either way their will be some initial squabbling. Especially if your current Angels have been in there alone for a long time. They see the entire tank as their territory. Adding any cichlid but particularly two more Angels will cause them to attempt to assert themselves and let those other fish know that they are the head honchos via chasing, biting, and charging. In a 55 G there should be enough space for the new Angels to stay out of the resident pairs way and as they grow maybe stake out an area of their own.
Whether it be Angels, Festivums, Rams, or a Red Terror there is no way that you can just add two new cichilds to an already established tank and not expect to see some intial chasing and charging. But it should subside.