I've not tried this with cyprichromis, but I've found with others that it's actually easier to add juvies because the adults don't see them as threats or competition for females, etc. But having said that, if you're planning to keep any fry you need to be absolutely sure that what you're adding is the exact same variant as what you have. Just because someone gives them a name doesn't necessarily make it so. Too easy to hybidize cyprichromis. A better option might be to move the 3 adults on and start over with a group of the juvies.