Buying three to four of the type you want to breed assures you of getting a pair. Then when they pair remove the other angels.
1) When you buy your breeders look at them closely to make sure the fins are straight, not frayed or split.
2)Then look at the gill plate covers they should cover the gills completely. Shortened or missing gill plate covers is a genetic defect and is passed on to fry.
3) Look at the body shape in general, does it look well rounded.
4) watch them swim a bit. do they swim right side up (many angels with swim bladder disease swim with their nose pointed up all the time)
5) are they eating eagerly?
Just a few things to look at when choosing angels to breed.
With a 125g I assume it's going to be a community tank. angels can get extremely aggressive to other tank mates(even in a large tank) when guarding eggs. fry will more ofter be eaten is there are other tankmates.
A twenty gallon tall makes a perfect breeding tank. Let them lay their eggs in that and then when fry hatch move mom and dad back to their bigger tank.
just some thoughts

Carol