Hi bigstinka
I've bred C. sterbai and found that they don't breed as young as the C. aeneus bronze or albino or C. paleatus do. If yours aren't breeding, perhaps they are just not ready yet. This is not unusual in corys.
They are not particularly difficult to breed, when they are mature, but I found that they do take a bit of encouragement. I breed my corys in 10 gallon tanks and when I get a good sized batch, I move the parents out, clean up the tank so it is bare bottom, and raise the young there until they are big enough to move up to a grow out tank. This reduces the loss that happens when you transfer the eggs.
Since the sterbai are warm water fish, keep their temperature of their breeding tank up around 80 degrees F. while you are conditioning them. Then when you want to cool the water, you can do it gently by turning off the heater for a while. Don't let it drop more than 5 degrees or so.
I've also found that they respond well if you agitate the water a bit at this time. They were one of the first corys I bred and while I was experimenting with it I noticed that they became quite excited when I did water changes, so I spent an entire evening dipping water up in a container and pouring it back into the tank. They loved it and spawned the following day. (I also unplugged the heater.) I don't know if it was the agitation itself or if it was the added oxygenation that resulted, but it worked for me that time. It's something you might try anyway. Perhaps an airstone would work as well.
Corys spawn well when they are in large groups and sometimes more than one female will be laying eggs, so if you want to keep all your sterbai together, you would need a tank larger than the 10 gallons I use. A 20 gallon or larger would be better.