The breeding pair needs 20 gallons on their own, I will put a smaller breeding pair in a 20 by themselves, a larger pair goes in a 29 with a few corys & a small plec. This is a standard stocking scheme for angels. In a pinch I will divide a 29 for two small pairs, that is considered overstocking.
If you look at the pair of gouramis as being the same bio load as a pair of angels you are overstocked, not by much as I see it, but overstocked nonetheless. Add in the rest of the fish, and it's a very busy tank. The stress added by a breeding pair only makes it worse.