With 4 angels in such a large tank you should find that if 2 pair off they will swim together for a lot of the time - which is another fasinating thing about them, and in my experience angels are very happy to be together in a group if they have grown up along-side each other.
Once you have a pair they will look for a suitable spawning ground in your tank, usually a long broad leaf or a high up slate - but more often or not in the most difficult places to cultivate the eggs, like on top of your filter, attatched to the glass, on the Co2 ladder etc. And once that suitable place is decided the pair will guard it for a while, do a bit of courting and eventually lay some eggs and fertilize them [it's important that you watch this as to decide which is male or female]. And from then on the eggs will be guarded, cleaned, removed if moldy, fanned [with the angels fin to circulate water around the eggs], which is when the pair will become a little fiesty towards other fish who happen to swim in that particular area of the tank - but the good thing is they won't leave the eggs for too long, so it's only for defence and no real harm will come of any tresspassing fish.
regards,
Paul.