Give them time. Imagine yourself being placed to hang out with a member of the opposite sex. How long before you'll hook up...?
Generally fish don't strike up an immediate attraction. I had 2 females and 1 male in my tank for about a month before they bred (male had been in for about 4 months before I added the two females).
Put a bit of slate in your tank at a shallow angle and they'll lay on it. It's a good place for it because the eggs stand out very clearly and you'll definitely know they have bred. The parents learn over time, and so the first few breedings might not go so well. My pair laid over 200 eggs, easily, but after 48 hours there were only about 30 left, and I actually watched the dad eat the last egg. Shame. But they'll learn.
If you don't have a slate, you'll be able to tell if you notice the two are hanging around together at one place constantly fanning their bottom fins - this is them keeping water moving around the eggs so as to not prevent disease.
There is no guarantee that your pair will breed. Rams have been known to stay with one partner, so if either has bred before this will limit the chance somewhat. Make sure you give them a varied diet with a focus on meaty foods although LIVE food over frozen is preferable if you are conditioning.
As far as overstocking is concerned, other fish WILL try to sneak a cheeky egg here and there - and will. This is stressful for the parents. Best to keep the tankmates down to a minimum.