It is too late, they've been bought!
Neons don't grow too big to be eaten by angels, they'll just pick at them.
And its v. easy to sex gourami, just google search female/male whichever and see how they compare. The male dorsal is very pointed, its very different,
Also, i have to disagree that angels and gouramies are good tankmates.
Angels are incredibly aggressive (depending on the individual) especially during spawning. they also patrol the top half of the tank, as do gourami. You might get away with it in a 55 gallon, due to the high volume, provide lots of hiding places for the gourami though, like bogwood and plants, if you do decide to keep them.