Hi,
OK can you tell us what weight the two snakes are? Because 2 and a half feet sounds waaay to small to be trying to breed a female ball python.
So what are the temps during the day and during the night?
What are you using the heat rock for - can you get the temps up to the recomended level using just the UTH and bulb?
It might be an idea to run through things with us a little more so we can give you better advice.
dr del